Semiconductor storage device with self-aligned opening and method for fabricating the same

ABSTRACT

A semiconductor device with a self-aligned opening and a method for fabricating the same, the semiconductor device including a first conductor pattern formed over a semiconductor substrate; a first insulation film formed over the first conductor pattern; a second insulation firm formed over the first insulation film, the second insulation film having a substantially flat surface and having etching characteristics different from those of the first insulation film; a third insulation film formed over the second insulation film, the third insulation film having etching characteristics different from those of the second insulation film; a fourth insulation film formed over the third insulation film, the fourth insulation film having etching characteristics different from those of the third insulation film; an opening formed in the fourth insulation film, the third insulation film, the second insulation film, and the first insulation film, the opening being self-aligned with the first conductor pattern, a second conductor pattern formed in the opening.

This application is a division of prior application Ser. No. 09/037,068,filed Mar. 9, 1998 now U.S. Pat. No. 6,395,599, which is a division ofapplication Ser. No. 08/592,481, filed Jan. 26, 1996, now U.S. Pat. No.5,874,756.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor storage device, morespecifically to a semiconductor storage device structure which enableshighly-integrated DRAMs (Dynamic Random Access Memories) to befabricated within tiny cell areas and by a small number of fabricationsteps, and a method for fabricating the semiconductor storage devicestructure.

A DRAM is a semiconductor storage device which can be formed of onetransistor and one capacitor. Various structures of the DRAM and variousmethods for fabricating the DRAM have been conventionally studied tofabricate semiconductor storage devices of higher density and higherintegration.

FIG. 59 shows a sectional view of the semiconductor storage devicedescribed in Japanese Patent Laid-Open Publication No. 176148/1986.

Source diffused layers 24 and drain diffused layers 26 are formed on asemiconductor substrate 10 independent of each other. Gate electrodes 20are formed, through gate oxide films 16, on parts of the semiconductorsubstrate 10 between the respective source diffused layers 24 and therespective drain diffused layers 26. Memory cell transistors thuscomprising the gate electrodes 20, the source diffused layers 24 and thedrain diffused layers 26 are constituted.

On the semiconductor substrate 10 with the memory cell transistorsformed thereon there are formed inter-layer insulation film 36 havingthrough-holes 38 which are opened on the drain diffused layers 26 andthrough-holes 40 which are opened on the source diffused layers 24.

Cylindrical capacitor storage electrodes 46 of polycrystalline siliconare formed on the inside walls of the through-holes 40 and have theirbottoms connected to the source diffused layers 24.

Capacitor dielectric films 48 are formed on the inside walls and uppersurfaces of the capacitor storage electrodes 46, and parts of the uppersurfaces of the source diffused layers 24 exposed inside thethrough-holes 40.

Capacitor opposed electrodes 54 are formed in the through-holes 40 withthe capacitor storage electrodes 46 and the capacitor dielectric films48 formed thereon, and on the inter-layer insulation film 36. Capacitorsthus comprising the capacitor storage electrodes 46, the capacitordielectric films 48 and the capacitor opposed electrodes 54 are formed.

Polycrystalline silicon is buried in the through-holes 38 and isconnected to bit lines 62 through an inter-layer insulation film 53formed on the capacitor opposed electrodes 54.

Furthermore, a metal wiring layer (not shown) is formed on the top ofthe bit lines through an inter-layer insulation film (not shown), and aDRAM comprising one-transistor and one-capacitor memory cells is formed.

FIG. 60 shows a sectional view of another semiconductor storage device.

Source diffused layers 24 and drain diffused layers 26 are formed on asemiconductor substrate 10 independent of each other. Gate electrodes 20are formed, through gate oxide films 16, on parts of the semiconductorsubstrate 10 between the source diffused layers 24 and the draindiffused layers 26. Memory cell transistors thus comprising the gateelectrodes 20, the source diffused layers 24 and the drain diffusedlayers 26 are constituted.

On the semiconductor substrate 10 with the memory cell transistorsformed thereon, there are formed inter-layer insulation film 102 havingthrough-holes 98 which are opened on the drain diffused layers 26 andthrough-holes 100 which are opened on the source diffused layers 24.Insulation films 42 are formed on the gate electrodes 20, covering thesame. Exposed parts of the insulation films 42 in the through-holes 98,100 are defined by the insulation films 42.

An inter-layer insulation film 36 is formed on the inter-layerinsulation film 102. Capacitor storage electrodes 46 of polycrystallinesilicon are formed on the inside walls and the bottoms of through-holes40 formed in the inter-layer insulation film 36. The capacitor storageelectrodes 46 are connected to the source diffused layers 24 throughpolycrystalline silicon films 104 buried in the through-holes 100.

Capacitor dielectric films 48 are formed on the inside surfaces and theupper surfaces of the capacitor storage electrodes 46. Capacitor opposedelectrodes 54 are formed in the through-holes 40 with the capacitorstorage electrodes 46 and the capacitor dielectric films 48 formedthereon, and on the inter-layer insulation film 36. Capacitors thuscomprising the capacitor storage electrodes 46, the capacitor dielectricfilms 48 and the capacitor opposed electrodes 54 are formed.

Polycrystalline silicon films 106 are buried in the through-holes 98 andare connected to bit lines 62 formed on the capacitor opposed electrodes54 through the inter-layer insulation film 53.

A metal wiring layer (not shown) is formed on the bit lines through aninter-layer insulation film (not shown), and a DRAM comprisingone-transistor and one-capacitor memory cells is formed.

To form DRAM cells, usually 9 lithography steps are necessary for theLOCOS isolation, the formation of the gate electrodes (word lines), thebit line contact holes, the bit lines, the through-holes for thecapacitor storage electrodes, the capacitor storage electrodes, thecapacitor opposed electrodes, the through-holes for the metal wiring,and the metal wiring.

In lithography steps, an alignment allowance for the gate electrodes andthe bit line contact holes, an alignment allowance for the gateelectrodes and the through-holes, and an alignment allowance for thethrough-holes and the bit lines are necessary, which makes the memorycell area accordingly larger.

To improve this disadvantage, the semiconductor storage device describedin Japanese Patent Laid-Open Publication No. 176148/1986 uses theabove-described structure, so that the capacitor storage electrodes areformed by self-alignment with the through-holes, whereby the lithographysteps are decreased by one step.

In the semiconductor storage device of FIG. 60, the capacitor storageelectrodes are formed by self-alignment, and in addition thereto thethrough-holes 98, 100 are formed by self-alignment with the gateelectrodes, whereby no alignment allowances for the gate electrodes andthe through-holes for the bit line contact and for the gate electrodesand the through-holes for the capacitor storage electrodes arenecessary. This can accordingly decrease the memory cell area.

The fabrication of a semiconductor storage device which can be highlyintegrated by a smaller number of lithography steps and with smalleralignment allowances has been thus proposed.

In the semiconductor storage device described in the specification ofJapanese Patent Laid-Open Publication No. 176148/1986, a polycrystallinesilicon film is deposited to form the capacitor storage electrodes 46,concurrently being buried in the through-holes 38, whereby theabove-described structure is formed. The reason for completely fillingthe through-holes is as follows.

As disclosed in the specification, the bit lines 62 are made ofaluminium (Al) and they thus are the uppermost wiring layer. Inaddition, to contact the Al to the source-drains or the gate electrodesfor peripheral circuits, it is necessary that the insulation film isetched by a larger thickness than a thickness of the bit line contact.The inter-layer insulation film 36 of the bit line contact, however, hasno trace of etching, and it is presumed that the peripheral circuitthrough-holes as well as the through-holes 38 are completely filled withpolycrystalline silicon.

The peripheral circuit through-holes are thus completely filled becausea contact resistance of a peripheral circuit greatly affects efficiencyof operation speed of the circuit, and preferably the through-holes arecompletely filled to reduce the contact resistance as much as possible.Accordingly, it is necessary to completely fill the bit line contactthrough-holes concurrently with filling the peripheral circuitthrough-holes.

In the semiconductor storage device disclosed in Japanese PatentLaid-Open Publication No. 176148/1986, the polycrystalline silicon filmburied in the peripheral circuit through-holes must be thicker than athrough-hole diameter. This is because since the capacitor storageelectrodes 46 are concurrently formed of the polycrystalline silicon,the polycrystalline silicon film of an excessive thickness will decreasean inside wall area of the through-holes 40, with a result of adecreased cell capacitance.

When the through-holes 38, 40 are formed, an alignment allowance for thegate electrodes 20 must be taken into consideration. This increases acell area and decreases a capacitor forming part.

In the semiconductor storage device of FIG. 60, as described above, theself-alignment contact is formed, and in forming the through-holes 98,100 it is not necessary to consider an alignment allowance for aligningthe through-holes 98, 100 with the gate electrode 20. The through-holes40 and the bit line contact hole 58 are formed separately from eachother, and the bit line contact holes 58 are not filled withpolycrystalline silicon. Accordingly, a capacitance does not decrease,as is described in the semiconductor storage device described inJapanese Patent Laid-Open Publication No. 176148/1986.

In the semiconductor storage device of FIG. 60, polycrystalline siliconis buried in the through-holes 98, 100 to connect the source diffusedlayers 24 to the capacitor storage electrodes 46, and the drain diffusedlayers 26 to the bit lines 62, and an extra lithography step of openingthe filled through-holes 98, 100 is needed. In comparison with thesemiconductor storage device described in Japanese Patent Laid-OpenPublication No. 176148/1986, one lithography step is added.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a semiconductor storagedevice and a method for fabricating the same which can decrease a memorycell area by decreasing an alignment allowance in lithography steps, andcan decrease a number of the lithography steps.

Another object of the present invention is to provide a semiconductorstorage device and a method for fabricating the same which canfacilitate etching the contact hole for the capacitor storage electrode,and can decrease a number of fabrication steps.

The above-described objects are achieved by a semiconductor storagedevice comprising: a memory cell including: a memory cell transistorhaving a first diffused layer and a second diffused layer formed in asemiconductor substrate, and a gate electrode formed through a gateinsulation film on the semiconductor substrate between the firstdiffused layer and the second diffused layer; a first insulation filmcovering an upper surface and side surfaces of the gate electrode; asecond insulation film covering a top of the memory cell transistor andhaving a first through-hole opened on the first diffused layer and asecond through-hole opened on the second diffused layer formed in; acapacitor having a capacitor storage electrode formed on inside wallsand a bottom of the first through-hole and connected to the firstdiffused layer, a capacitor dielectric film formed covering thecapacitor storage electrode, and a capacitor opposed electrode formedcovering at least a part of the capacitor dielectric film; and a firstcontact conducting film formed on inside walls and a bottom of thesecond through-hole and connected to the second diffused layer; a thirdinsulation film formed on the memory cell and having a bit line contacthole formed in; and a bit line formed on the third insulation film andconnected to the first contact conducting film of the memory cellthrough the bit line contact hole. This structure of the semiconductorstorage device makes it unnecessary to secure an alignment allowance foralignment of the first through-hole opened on the first diffused layerand the second through-hole opened on the second diffused layer with thegate electrode, which permits the semiconductor storage device to havesmall memory cell area. It is not necessary to bury the first contactconducting film completely in the second through-hole, which makes itunnecessary to excessively increase the thickness of the capacitorstorage electrode, and decrease of the capacitance can be prevented.

The above-described objects are achieved also by a semiconductor storagedevice comprising: a memory cell including: a memory cell transistorhaving a first diffused layer and a second diffused layer formed in asemiconductor substrate, and a gate electrode formed through a gateinsulation film on the semiconductor substrate between the firstdiffused layer and the second diffused layer; a first insulation filmcovering an upper surface and side surfaces of the gate electrode; asecond insulation film covering a top of the memory cell transistor andhaving a first through-hole opened on the first diffused layer and asecond through-hole opened on the second diffused layer formed in; afirst buried conductor buried on a bottom of the first through-hole andconnected to the first diffused layer; a second buried conductor buriedon a bottom of the second through-hole and connected to the seconddiffused layer; and a capacitor having a capacitor storage electrodeformed on inside walls of the first through-hole and an upper surface ofthe first buried conductor and connected to the first diffused layerthrough the first buried conductor, a capacitor dielectric film formedcovering the capacitor storage electrode, and a capacitor opposedelectrode formed covering at least a part of the capacitor dielectricfilm; and a first contact conducting film formed on inside walls of thesecond through-hole and an upper surface of the second buried conductorand connected to the second diffused layer through the second buriedconductor; a third insulation film formed on the memory cell and havinga bit line contact hole formed in; and a bit line formed on the thirdinsulation film and connected to the first contact conducting film ofthe memory cell through the bit line contact hole. In this structure ofthe semiconductor storage device, in forming the through-holes, etc.having high aspect ratios, buried conductors of low resistance arebeforehand formed in the region contacting the semiconductor substrateto form an ohmic contact. This ensures contact characteristics at thebottoms of the through-holes even in a case that the through-holes havea higher aspect ratio as the device are higher integrated.

The above-described objects can be achieved also by a semiconductorstorage device comprising: a memory cell including: a memory celltransistor having a first diffused layer and a second diffused layerformed in a semiconductor substrate, and a gate electrode formed througha gate insulation film an the semiconductor substrate between the firstdiffused layer and the second diffused layer; a second insulation filmcovering a top of the memory cell transistor, and having a firstthrough-hole opened on the first diffused layer, a second through-holeopened on the second diffused layer and an opening having a largeropening diameter than the first through-hole and formed in a regionspaced from the semiconductor substrate, surrounding the firstthrough-hole; a capacitor having a capacitor storage electrode formed oninside walls and a bottom of the opening and on inside walls and abottom of the first through-hole, a capacitor dielectric film formedcovering the capacitor storage electrode, and a capacitor opposedelectrode, covering at least a part of the capacitor dielectric film;and a first contact conducting film formed on inside walls and a bottomof the second through-hole and connected to the second diffused layer; athird insulation film formed on the memory cell and having a bit linecontact hole formed in; and a bit line formed on the third insulationfilm and connected to the first contact conductor film of the memorycell through the bit line contact hole. This structure of thesemiconductor storage device makes it possible to make the openingdiameter of the through-holes very small without decrease of acapacitance, whereby short-circuit between the bit lines and the wordlines due to dust staying in the through-holes can be prevented.

In the above-described semiconductor storage device, it is preferablethat the capacitor storage electrode has a first columnar conductorformed in the first through-hole, spaced from the inside walls of thefirst through-hole; and the first contact conducting film has a secondcolumnar conductor formed in the second through-hole, spaced from theinside walls of the second through-hole. The first columnar conductoralso functions as the capacitor storage electrodes, whereby thecapacitance can be drastically increased. The wiring between the seconddiffused layer and the bit line is formed of the first contactconducting film and the second columnar conductor, whereby the wiringresistance of the wiring between the second diffused layer to the bitline can be decreased.

In the above-described semiconductor storage device, it is preferablethat the second insulation film in a region contacting the firstinsulation film is formed of a material having etching characteristicsdifferent from those of the first insulation film. In this structure ofthe semiconductor storage device, the first insulation film can be usedas an etching stopper in opening the through-holes, and the openings onthe substrate can be formed by self-alignment. Accordingly, it is notnecessary to ensure an alignment allowance with the gate electrode informing the through-holes. The semiconductor storage device can have asmall memory cell area.

In the above-described semiconductor storage device, it is preferablethat the first insulation film is silicon nitride film; and the materialhaving etching characteristics different from those of the firstinsulation film is silicon oxide film or impurity-doped silicon oxidefilm.

In the above-described semiconductor storage device, it is preferablethat the capacitor storage electrode further includes a columnarconductor projected in a column-shape in the opening out of the firstthrough-hole, whereby the capacitor storage electrode has an increasedarea by that of the columnar conductor, and an increased capacitance canbe obtained.

In the above-described semiconductor storage device, it is preferablethat the device further comprises a sidewall insulation film formed onthe inside walls of the bit line contact hole; and the bit line isinsulated with respect to the capacitor opposed electrode by thesidewall insulation film. The structure of the semiconductor storagedevice permits the lithography step of forming the capacitor opposedelectrode and the lithography step of forming the bit line contact holeto be concurrently conducted.

In the above-described semiconductor storage device, it is preferablethat the device further comprises a peripheral circuit transistor formedon the semiconductor substrate on a periphery of a memory cell regionwhere the memory cell is formed, and a wiring layer formed on the secondinsulation film and formed of the same conducting layer as the bit line;and the wiring layer is directly connected to a gate electrode, a firstdiffused layer or a second diffused layer of the peripheral circuittransistor. This structure of the semiconductor storage device permitsthe above-described semiconductor storage device to be fabricatedwithout sacrificing operational speeds of peripheral circuits.

In the above-described semiconductor storage device, it is preferablethat the device further comprises a peripheral circuit transistor formedon the semiconductor substrate on a periphery of the memory cell regionwhere the memory cell is formed, a fourth insulation film formed on thebit line, and a wiring layer formed on the fourth insulation film; andin which the wiring layer is directly connected to a gate electrode, afirst diffused layer or a second diffused layer of the peripheralcircuit transistor. This structure of the semiconductor storage devicepermits the semiconductor storage device to be fabricated without addingto the number of steps of the fabrication and without sacrificingoperational speeds of peripheral circuits.

In the above-described semiconductor storage device, it is preferablethat the wiring layer is directly connected to the gate electrode, thefirst diffused layer or the second diffused layer of the peripheralcircuit transistor, the capacitor opposed electrode, or the bit line.This structure of the semiconductor storage device permits thesemiconductor storage device to be fabricated without adding to thenumber of steps of the fabrication and without sacrificing operationalspeeds of peripheral circuits.

In the above-described semiconductor storage device, it is preferablethat the device further comprises an etching protection pattern provideddirectly below the bit line in a region where the bit line and thewiring layer are connected to each other and having the same structureof a laminated film of the capacitor opposed electrode and the thirdinsulation film. This structure of the semiconductor storage deviceallows the deep through-holes formed in the peripheral circuit regionand the shallow through-holes formed on the bit lines or the capacitoropposed electrodes to be concurrently opened without generatingshort-circuits between the bit line and the semiconductor substrate.

In the above-described semiconductor storage device, it is preferablethat the device further comprises a peripheral circuit transistor formedon the semiconductor substrate on a periphery of the memory cell regionwhere the memory cell is formed, and a wiring layer formed on the thirdinsulation film and formed of the same conducting layer as the bit line;and in which the capacitor opposed electrode and the third insulationfilm are formed extended in a region where the peripheral circuittransistor is formed, and the wiring layer is directly connected to agate electrode, a first diffused layer or a second diffused layer of theperipheral circuit transistor. This structure of the semiconductorstorage device makes it possible to form the wiring layers of peripheralcircuits without adding to the number of fabrication steps.

In the above-described semiconductor storage device, it is preferablethat the device further comprises a peripheral circuit transistor formedon the semiconductor substrate on a periphery of the memory cell regionwhere the memory cell is formed, and a second contact conductor filmformed on inside walls and a bottom of a third through-hole formed inthe second insulation film on a gate electrode, a first diffused layeror a second diffused layer of the peripheral circuit transistor; and inwhich the gate electrode, the first diffused layer or the seconddiffused layer of the peripheral circuit transistors are connected,through the second contact conducting film, to a wiring layer formed onthe second insulation film. This structure of the semiconductor storagedevice makes it possible to fabricate the above-described semiconductorstorage device without adding to the number of fabrication steps.

In the above-described semiconductor storage device, it is preferablethat the device further comprises a third buried conductor formed on abottom of the third through-hole; and in which the second contactconducting film is connected to the gate electrode, the first diffusedlayer or the second diffused layer of the peripheral circuit transistorthrough the third buried conductor. In this structure of thesemiconductor storage device, in forming the through-holes, etc. havinghigh aspect ratios, buried conductors of low resistance are beforehandformed in the region contacting the semiconductor substrate to form anohmic contact. This ensures good contact characteristics at the bottomsof the through-holes even in a case that the through-holes have a higheraspect ratio as the device becomes more higher integrated.

In the above-described semiconductor storage device, it is preferablethat the second insulation film is a laminated film of a plurality ofinsulation materials having different etching characteristics from eachother. This structure of the semiconductor storage device makes it easyto open the through-holes even when the through-holes have a high aspectratio.

In the above-described semiconductor storage device, it is preferablethat the laminated film comprises a silicon nitride film, and siliconoxide films sandwiching the silicon nitride film.

In the above-described semiconductor storage device, it is preferablethat the laminated film comprises a silicon nitride film laid on asilicon oxide film.

The above-described objects can be achieved also by a semiconductorstorage device comprising: a memory cell including: a memory celltransistor having a first diffused layer and a second diffused layerformed in a semiconductor substrate, and a gate electrode formed througha gate insulation film on the semiconductor substrate between the firstdiffused layer and the second diffused layer; a first insulation filmcovering an upper surface and side surfaces of the gate electrode; asecond insulation film covering a top of the memory cell transistor andhaving a first through-hole opened on the first diffused layer; and acapacitor having a capacitor storage electrode having contact formed oninside walls and a bottom of the first through-hole and connected to thefirst diffused layer and having a projection formed projecting on thesecond insulation film and connected to the contact, a capacitordielectric film formed covering the capacitor storage electrode, and acapacitor opposed electrode formed covering at least a part of thecapacitor dielectric film. This structure of the semiconductor storagedevice permits constituting the capacitor with the inside walls and theoutside walls of the projection, which can increase the capacitance.

In the above-described semiconductor storage device, it is preferablethat the device further comprises a third insulation film formed on thememory cell and having bit line contact hole reaching the seconddiffused layer through the second insulation film formed in; and a bitline formed on the third insulation film and connected to the seconddiffused layer of the memory cell through the bit line contact hole.

In the above-described semiconductor storage device, it is preferablethat a second through-hole is formed in the second insulation film andis opened on the second diffused layer; and which further comprises acontact conducting film formed on inside walls and a bottom of thesecond through-hole and connected to the second diffused layer, and abit line formed on the memory cell through the third insulation film andconnected to the contact conducting film.

In the above-described semiconductor storage device, it is preferablethat the second insulation film comprises a silicon nitride film and asilicon oxide film; the silicon nitride film is formed on the gateelectrode; the silicon oxide film is formed on the silicon nitride film;and the third insulation film comprises a silicon oxide film. Thisstructure of the semiconductor storage device makes it easy to form theprojection, and capacitance deviations can be reduced.

In the above-described semiconductor storage device, it is preferablethat the first contact conducting film, the second contact conductingfilm or the capacitor storage electrode are formed of a conductingmaterial which contacts n-silicon and p-silicon. This structure of thesemiconductor storage device can improve contact characteristics withthe silicon substrate as the semiconductor substrate.

In the above-described semiconductor storage device, it is preferablethat the bit line contact hole is elongated in the direction of the bitline. This structure of the semiconductor storage device allows the bitlines and the word lines to be arranged in minimum process dimensions.The semiconductor storage device can have a small memory cell area.

In the above-described semiconductor storage device, it is preferablethat the bit line has a film thickness which is below half a gap betweenthe bit lines. This structure of the semiconductor storage device allowscapacity coupling between the bit lines to be reduced.

The above-described objects can be achieved also by a semiconductorstorage device comprising: a plurality of bit lines arranged parallelwith each other; a plurality of word lines arranged parallel with eachother and intersecting said plurality of bit lines; sense amplifiersdisposed on one end of the respective bit lines; decoders disposed onone end of the respective word lines; and above-described memory cellsrespectively disposed at intersections of the bit lines and the wordlines; said plural sense amplifiers being divided into two groups, thegroups of the sense amplifiers being disposed respectively on opposedsides of a memory cell region where the memory cells are formed; saidplural decoders being divided into two groups, the groups of thedecoders being disposed respectively on opposed sides of the memory cellregion where the memory cells are formed. This structure of thesemiconductor storage device allows a peripheral circuit to be connectedto the bit lines and the word lines to be arranged with minimumprocessing dimensions.

The above-described objects can be achieved also by a semiconductorstorage device comprising: a memory cell including: a memory celltransistor having a first diffused layer and a second diffused layerformed in a semiconductor substrate, and a gate electrode formed througha gate insulation film on the semiconductor substrate between the firstdiffused layer and the second diffused layer; a second insulation filmcovering a top of the memory cell transistor and having a firstthrough-hole opened on the first diffused layer and a secondthrough-hole opened on the second diffused layer; a buried conductorburied in the first through-hole: and a capacitor having a capacitorstorage electrode formed on the second insulation film and connected tothe first diffused layer through the buried conductor, a capacitordielectric film formed covering the capacitor storage electrode and acapacitor opposed electrode formed covering at least a part of thecapacitor dielectric film; and a bit line formed on the secondinsulation film and connected to the second diffused layer through thesecond through-hole; the buried conductor and the bit line being formedof the same conducting layer. This structure of the semiconductorstorage device can reduce the etching time for opening the through-holesfor contact with the capacitor storage electrode, whereby the exposureof the bit line in the etching can be prevented.

In the above-described semiconductor storage device, it is preferablethat the buried conductor is formed on sidewalls and a bottom of thefirst through-hole.

In the above-described semiconductor storage device, it is preferablethat the first through-hole and the second through-hole are formedspaced outward from the gate electrode.

In the above-described semiconductor storage device, is preferable thatan upper surface and side surfaces of the bit line are covered with afirst insulation film which functions as an etching stopper with respectto a third insulation film formed on the bit line. This structure of thesemiconductor storage device can reduce damage to the bit line inopening the through-hole for contact with the capacitor storageelectrode.

In the above-described semiconductor storage device, it is preferablethat the third insulation film has a third through-hole formed in, theburied conductor being exposed in the third through-hole; and thecapacitor dielectric film is formed on sidewalls and a bottom of thethird through-hole. This structure of the semiconductor storage devicecan reduce the height difference between the peripheral circuit regionand the memory cell region, which permits the design rule of the wiringlayers formed thereabove to be reduced.

The above-described objects can be achieved also by a semiconductorstorage device comprising: a memory cell including: a memory celltransistor having a first diffused layer and a second diffused layerformed in a semiconductor substrate, and a gate electrode formed througha gate insulation film on the semiconductor substrate between the firstdiffused layer and the second diffused layer; a first insulation filmcovering a top of the memory cell transistor and having a firstthrough-hole opened on the first diffused layer and a secondthrough-hole opened on the second diffused layer; a buried conductorburied in the first through-hole: and a capacitor having a capacitorstorage electrode formed on the first insulation film and connected tothe first diffused layer through the buried conductor, a capacitordielectric film formed covering the capacitor storage electrode and acapacitor opposed electrode formed covering at least a part of thecapacitor dielectric film; and a bit line formed on the first insulationfilm and connected to the second diffused layer through the secondthrough-hole; the buried conductor and the bit line being formed of thesame conducting layer. This structure of the semiconductor storagedevice can reduce the etching time for opening the through-holes forcontact with the capacitor storage electrode, whereby the exposure ofthe bit line in the etching can be prevented.

In the above-described semiconductor storage device, it is preferablethat the buried conductor is formed on sidewalls and a bottom of thefirst through-hole.

In the above-described semiconductor storage device, it is preferablethat the first through-hole and the second through-hole are formedspaced outward from the gate electrode.

In the above-described semiconductor storage device, is preferable thatan upper surface and side surfaces of the bit line are covered with aninsulation film which functions as an etching stopper with respect to asecond insulation film formed on the bit line. This structure of thesemiconductor storage device can reduce damage to the bit line inopening the through-hole for contact with the capacitor storageelectrode.

In the above-described semiconductor storage device, it is preferablethat the second insulation film has a third through-hole formed in, theburied conductor being exposed in the third through-hole; and thecapacitor dielectric film is formed on sidewalls and a bottom of thethird through-hole. This structure of the semiconductor storage devicecan reduce the height difference between the peripheral circuit regionand the memory cell region, which permits the design rule of the wiringlayers formed thereabove to be reduced.

The above-described objects can be achieved also by a method forfabricating a semiconductor storage device comprising: a gate electrodeforming step of depositing a first conducting film and a firstinsulation film the latter on the former on a semiconductor substrateand then patterning the first conducting film and the first insulationfilm to form gate electrodes formed of the first conducting film andhaving upper surfaces covered with the first insulation film; a diffusedlayer forming step of doping the semiconductor substrate with animpurity with the gate electrodes as a mask to form first diffusedlayers and second diffused layers; a first sidewall insulation filmforming step of forming first sidewall insulation films on sidewalls ofthe gate electrodes; a first insulation film forming step of forming asecond insulation film having first through-holes and secondthrough-holes formed in, the first through-holes being opened on thefirst diffused layer, the second through-holes being opened on thesecond diffused layer; a second conducting film depositing step ofdepositing a second conducting film on the semiconductor substratehaving the second insulation film formed on; a conducting film removingstep of removing the second conducting film on the second insulationfilm, leaving the second conducting film in the first through-holes andthe second through-holes to form capacitor storage electrodes of thesecond conducting film in the first through-holes and first contactconducting films of the second conducting film formed in the secondthrough-holes; and a capacitor opposed electrode forming step ofdepositing a third insulation film to be capacitor dielectric films anda third conducting film to be capacitor opposed electrodes on thesemiconductor substrate with the capacitor storage electrodes and thefirst contact conducting film and then patterning the third conductingfilm to form the capacitor opposed electrodes. The method forfabricating a semiconductor storage device enables the semiconductorstorage device having a small memory cell area to be fabricated withoutincreasing the electric resistance between the bit lines and the seconddiffused layers and without decreasing the capacitance.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that in the capacitor opposed electrode formingstep, a fourth insulation film deposited on the third conducting filmand the third conducting film are patterned to form the capacitoropposed electrodes and bit line contact holes opened on the secondthrough-holes; and which further comprises a second sidewall insulationfilm forming step of depositing a fifth insulation film after thecapacitor opposed electrode forming step and anisotropically etching thefifth insulation film for second sidewall insulation films on insidewalls of the bit line contact holes while concurrently therewithremoving the third insulation films on bottoms of the bit line contactholes; and a bit line forming step of forming bit lines formed on thefourth insulation film and connected to the first contact conductingfilm exposed in the bit line contact holes. This method permits thelithography step of forming the capacitor opposed electrodes and thelithography step of forming the bit line contact holes to besimultaneously conducted.

The above-described objects can be achieved also by a method forfabricating a semiconductor storage device comprising: a gate electrodeforming step of depositing a first conducting film and a firstinsulation film the latter on the former on a semiconductor substrateand then patterning the first conducting film and the first insulationfilm to form first gate electrodes of the first conducting film havingupper surfaces covered with the first insulation film in a first regionfor memory cell transistors to be formed in and second gate electrodesof the first conducting film having upper surfaces covered with thefirst insulation film in a second region for peripheral circuittransistors to be formed in; a diffused layer forming step of doping thesemiconductor substrate with an impurity with the gate electrodes as amask to form in the first region first diffused layers and seconddiffused layers of the memory cell transistors and in the second regionfirst diffused layers and second diffused layers of the peripheralcircuit transistors; a first sidewall insulation film forming step offorming first sidewall insulation films on sidewalls of the gateelectrodes; a first insulation film forming step of forming a secondinsulation film having first through-holes and second through-holesformed in, the first through-holes being opened on the first diffusedlayer of the memory cell transistors, the second through-holes beingopened on the second diffused layers of the memory cell transistors; asecond conducting film depositing step of depositing a second conductingfilm on the semiconductor substrate having the second insulation filmformed on; a conducting film removing step of removing the secondconducting film on the second insulation film, leaving the secondconducting film in the first through-holes and the second through-holesto form capacitor storage electrodes of the second conducting filmformed in the first through-holes and the first contact conducting filmof the second conducting film formed in the second through-holes; a bitline contact hole forming step of depositing a third insulation film tobe capacitor dielectric films, a third conducting film to be capacitoropposed electrodes and a fourth insulation film on the capacitor storageelectrodes and the first contact conducting film and then patterning thefourth insulation film and the third conducting film to form thecapacitor opposed electrodes and bit line contact holes opened on thesecond through-holes; a second sidewall insulation film forming step ofdepositing a fifth insulation film on the fourth insulation film withthe bit line contact holes and then anisotropically etching the fifthinsulation film to form second sidewall insulation films on inside wallsof the bit line contact holes while concurrently therewith removing thethird insulation film on bottoms of the bit line contact holes; a secondthrough-hole forming step of forming third through-holes opened on thefourth insulation film on the capacitor opposed electrodes and fourththrough-holes formed in the second insulation film opened on the firstdiffused layers or the second diffused layers of the peripheral circuittransistors, or the second gate electrodes; and a wiring layer formingstep of forming bit lines connected to the first contact conducting filmexposed in the bit line contact holes, first wiring layers connected tothe capacitor opposed electrodes through the third through-hole andsecond wiring layers connected to the peripheral circuit transistorsthrough the fourth through-holes. This method allows the semiconductorstorage device to be fabricated without sacrificing operational speedsof peripheral circuits.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that the method further comprises: after thesecond sidewall insulation film forming step, a bit line forming step offorming bit lines connected to the contact conducting film exposed inthe bit line contact holes, a second insulation film forming step offorming a sixth insulation film on the semiconductor substrate with thebit line formed thereon; and in which in the second through-hole formingstep, third through-holes reaching the capacitor opposed electrodes areformed in the sixth insulation film and the fourth insulation film, andfourth through-holes reaching the first diffused layers or the seconddiffused layers of the peripheral circuit transistors, or the secondgate electrodes are formed in the sixth insulation film and the secondinsulation film; and in the wiring layer forming step, first wiringlayers connected to the capacitor opposed electrodes through the thirdthrough-holes, and second wiring layers connected to the peripheralcircuit transistors through the fourth through-holes are formed. Thismethod can fabricate the semiconductor storage device without adding tothe number of fabrication steps and sacrificing operational speedsperipheral circuits.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that in the second through-hole forming step,when fifth through-holes for connecting the bit lines and the wiringlayers are formed, in the bit line contact hole forming step, an etchingprotection pattern of the laminated film of the third conducting filmand the fourth insulation film is formed on the second insulation filmin a region where contact holes for connecting the bit lines and thewiring layers are to be formed. This method can prevent etching of thesecond insulation film directly below the bit lines even in opening thedeep through-holes in the peripheral circuit region, wherebyshort-circuit between the bit lines and the semiconductor substrate canbe prevented.

The above-described objects can be achieved also by a method forfabricating a semiconductor storage device comprising: a gate electrodeforming step of depositing a first conducting film and a firstinsulation film the latter on the former on a semiconductor substrateand then patterning the first conducting film and the first insulationfilm to form first gate electrodes of the first conducting film havingupper surfaces covered with the first insulation film in a first regionwhere memory cell transistors are to be formed and second gateelectrodes having upper surfaces covered with the first insulation filmin a second region where peripheral circuit transistors are to beformed; a diffused layer forming step of doping the semiconductorsubstrate with an impurity with the gate electrodes as a mask to formfirst diffused layers and second diffused layers of the memory celltransistors in the first region and first diffused layers and seconddiffused layers of the peripheral circuit transistors in the secondregion; a first sidewall insulation film forming step of forming firstsidewall insulation films on sidewalls of the gate electrodes; a firstinsulation film forming step of forming a second insulation film havingfirst through-holes and second through-holes formed in, the firstthrough-holes being opened on the first diffused layers of the memorycell transistors, the second through-holes being opened on the seconddiffused layers of the memory cell transistors; a second conducting filmdepositing step of depositing a second conducting film on thesemiconductor substrate having the second insulation film formed on; aconducting film removing step of removing the second conducting film onthe second insulation film, leaving the second conducting film in thefirst through-holes and the second through-holes to form capacitorstorage electrodes of the second conducting film formed in the firstthrough-holes and first contact conducting film of the second conductingfilm formed in the second through-holes; a bit line contact hole formingstep of depositing a third insulation film to be capacitor dielectricfilms, a third conducting film to be capacitor opposed electrodes and afourth insulation film on the capacitor storage electrodes and the firstcontact conducting film and then patterning the fourth insulation filmand the third conducting film to form the capacitor opposed electrodesand bit line contact holes opened on the second through-holes and toopen third through-holes onto the third insulation film which are to beopened on the first diffused layers or the second diffused layers of theperipheral circuit transistors or the second gate electrodes; and asecond through-hole forming step of selectively forming a photo-resistcovering the bit line contact holes and then etching the thirdinsulation film in the third through-holes and the second insulationfilm to form the third through-holes extending to the first diffusedlayers or the second diffused layers of the peripheral circuittransistors or the second gate electrodes. This method requires nosubtle alignment in opening the through-holes in the peripheral circuitregion, which simplifies the lithography steps.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that the bit line contact hole forming step,the third insulation film to be capacitor dielectric films, the thirdconducting film to be capacitor opposed electrodes, the fourthinsulation film and a mask film functioning as an etching stopper aresuccessively deposited on the capacitor storage electrodes and thesecond conducting film, and then the mask film, the fourth insulationfilm and the third conducting film are patterned, to form the capacitoropposed electrodes and bit line contact holes opened on the secondthrough-holes, and to open onto the third insulation film the thirdthrough-holes which are to be opened on the first diffused layers or thesecond diffused layers of the peripheral circuit transistors or thesecond gate electrodes; and in the second through-hole forming step, aphoto-resist for covering the bit line contact holes is selectivelyformed, and then with the mask film and the photo-resist as an etchingmask, the third insulation film in the third through-holes and thesecond insulation film are etched to form the third through-holesextending to the first diffused layers or the second diffused layers ofthe peripheral circuit transistors or the second gate electrodes. Thismethod can simplify the lithography steps.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that the mask film is silicon film.

The above-described objects can be achieved also by a method forfabricating a semiconductor storage device comprising: a gate electrodeforming step of depositing a first conducting film and a firstinsulation film the latter on the former on a semiconductor substrateand then patterning the first conducting film and the first insulationfilm to form first gate electrodes of the first conducting film havingupper surfaces covered with the first insulation films in a first regionwhere memory cell transistors are to be formed and to form second gateelectrodes of the first conducting film having upper surfaces coveredwith the first insulation film in a second region where peripheralcircuit transistors are to be formed; a diffused layer forming step ofdoping the semiconductor substrate with an impurity with the gateelectrodes as a mask to form first diffused layers and second diffusedlayers of the memory cell transistors in the first region and to formfirst diffused layers and second diffused layers of the peripheralcircuit transistors in the second region; a first sidewall insulationfilm forming step of forming first sidewall insulation films onsidewalls of the gate electrodes; a first insulation film forming stepof forming a second insulation film having first-through holes, secondthrough-holes, and third through-holes formed in, the firstthrough-holes being opened on the first diffused layers of the memorycell transistors, the second through-holes being opened on the seconddiffused layers of the memory cell transistors and the thirdthrough-holes opened on the first diffused layer or the second diffusedlayers of the peripheral circuit transistors or the second gateelectrodes; a second conducting film depositing step of depositing asecond conducting film on the semiconductor substrate having the secondinsulation film formed on; a conducting film removing step of removingthe second conducting film on the second insulation film, leaving thesecond conducting film in the first through-holes, the secondthrough-holes and the third through-holes to form capacitor storageelectrodes of the second conducting film formed in the firstthrough-holes, first contact conducting films of the second conductingfilm formed in the second through-holes and second contact conductingfilms of the second conducting film formed in the third through-holes; abit line contact hole forming step of depositing a third insulation filmto be capacitor dielectric films, a third conducting film to becapacitor opposed electrodes and a fourth insulation film on thesemiconductor substrate with the capacitor storage electrodes, the firstcontact conducting films and the second contact conducting films formedon and then patterning the fourth insulation film and the thirdconducting film to form the capacitor opposed electrodes and bit linecontact holes opened on the second through-holes; a second sidewallinsulation film forming step of depositing a fifth insulation film onthe fourth insulation film with the bit line contact holes formed in andthen anisotropically etching the fifth insulation film to form secondsidewall insulation films on inside walls of the bit line contact holeswhile concurrently therewith removing the third insulation film onbottoms of the bit line contact holes; and a wiring layer forming stepof forming bit lines connected to the first contact conducting filmsexposed in the bit line contact holes and wiring layers connected to thesecond contact conducting films formed in the third through-holes. Thismethod can fabricate the semiconductor storage device without adding tothe number of fabrication steps.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that in the capacitor opposed electrode formingstep, a third conducting film is buried in the first through-holes orthe second through-holes to planarize a surface of the third conductingfilm. This method can simultaneously conduct the lithography step offorming the capacitor opposed electrodes and the lithography step offorming the bit line contact holes.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that the method further comprises: after thesecond conducting film depositing step, a third sidewall insulation filmforming step of depositing a seventh insulation film and anisotropicallyetching the seventh insulation film to form third sidewall insulationfilms on inside walls of the first through-holes and the secondthrough-holes with the second conducting film formed thereon, and afourth conducting film depositing step of depositing a fourth conductingfilm to fill the first through-holes and the second through-holes havingthe third sidewall insulation films formed on; and further comprising:after the conducting film removing step, a columnar conductor formingstep of removing the third sidewall insulation film to form firstcolumnar conductors of the fourth conducting film in the firstthrough-holes and second columnar conductors of the fourth conductingfilm in the second through-holes, in the conducting film removing step,the fourth conducting film, the second conducting film and the secondinsulation film are removed until surfaces of the third sidewallinsulation films are exposed. This method can fabricate the firstcolumnar conductors so as to function as the capacitor storageelectrodes and the second columnar conductors so as to function as thewiring between the second diffused layers and the bit lines, whereby thecapacitance can be drastically increased and the wiring resistance ofthe wiring between the second diffused layers-the bit lines can bedecreased. This method can also prevent, in polishing the secondconducting film, the polishing agent, etc. from intruding into thethrough-holes, whereby resultant low yields can be precluded.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that in the first insulation film forming step,a second insulation film is deposited and then is polished to planarizea surface of the second insulation film before the through-holes areformed. This method can improve the global planarization on the secondinsulation film, whereby the depth of focus for opening thethrough-holes can be small, and micronized patterns can be made.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that in the conducting film removing step, asurface of the semiconductor substrate is polished to remove the secondconducting film on the second insulation film. This method can easilyform the capacitor storage electrodes and the contact conducting filmshaving the through-holes whose configurations are aligned.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that in the first insulation film forming step,a second insulation film is formed of a laminated film of a plurality ofinsulation materials having different etching characteristics from eachother, and the insulation materials are etched one by one to open thethrough-holes. This method can easily open through-holes having highaspect ratios.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that the method further comprises: after thesecond conducting film depositing step, a photo-resist application stepof applying a photo-resist to the second conducting film to fill thefirst through-holes, the second through-holes or the thirdthrough-holes; and after the conducting film removing step, aphoto-resist releasing step of releasing the photo-resist buried in thethrough-holes, the second through-holes or the third through-holes,inthe conducting film removing step, the second conducting film and thephoto-resist on the second insulation film are removed, leaving thesecond conducting film and the photo-resist in the first through-holes,the second through-holes or the third through-holes. This method canprevent, in polishing the second conducting film, the polishing agent,etc. from intruding into the through-holes, whereby resultant low yieldscan be precluded.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that the method further comprises: after thesecond conducting film depositing step, an insulation film depositingstep of depositing a eighth insulation film having etchingcharacteristics different from those of the second insulation film tofill the first through-holes the second through-holes or the thirdthrough-holes; after the conducting film removing step, an insulationfilm removing step of removing the eighth insulation film buried in thefirst through-holes, the second through-holes or the thirdthrough-holes, in the conducting film removing step, a second conductingfilm and the eighth insulation film on the second insulation film areremoved, leaving the second conducting film and the eighth insulationfilm in the first through-holes, the second through-holes and thirdthrough-holes. This method can prevent, in polishing the secondconducting film, the polishing agent, etc. from intruding into thethrough-holes, whereby resultant low yields can be precluded.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that the second insulation film is a laminatedfilm having an insulation film having on a surface thereof etchingcharacteristics different from those of the eighth insulation film. Thismethod makes it possible to selectively remove, after the polishing,only the insulation film buried in the through-holes.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that the method further comprises: after thesecond conducting film depositing step, an insulation film depositingstep of depositing a eighth insulation film having etchingcharacteristics substantially the same as those of the second insulationfilm to fill the first through-holes, the second through-holes or thethird through-holes; and after the conducting film removing step, aninsulation film removing step of removing the eighth insulation filmburied in first through-holes, the second through-holes or the thirdthrough-holes, leaving the second conducting film and the eighthinsulation film in the first through-holes, the second through-hole orthe third through-holes. This method can prevent, in polishing thesecond conducting film, the polishing agent, etc. from intruding intothe through-holes, whereby resultant low yields can be precluded.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that the second insulation film is a laminatedfilm of an insulation film having substantially the same etchingcharacteristics as those of the eighth insulation film deposited on aninsulation film having etching characteristics different from those ofthe eighth insulation film,in the insulation film removing step a eighthinsulation film and the insulation film having substantially the sameetching characteristics are removed. This method makes it possible toselectively remove, in the insulation film removing step, the eighthinsulation film and the insulation film having substantially the sameetching characteristics as the eighth insulation film.

The above-described objects can be achieved also by a method forfabricating a semiconductor storage device comprising: a gate electrodeforming step of depositing a first conducting film and a firstinsulation film the latter on the former on a semiconductor substrateand then patterning the first conducting film and the first insulationfilm to form first gate electrodes of the first conducting film havingupper surfaces covered with the first insulation film in a first regionwhere memory cell transistors are to be formed, and second gateelectrodes of the first conducting film having upper surfaces coveredwith the first insulation film in a second region where peripheralcircuit transistors are to be formed; a diffused layer forming step ofdoping the semiconductor substrate with an impurity with the gateelectrodes as a mask to form first diffused layers and second diffusedlayers of the memory cell transistors in the first region, and firstdiffused layers and second diffused layers of the peripheral circuittransistors in the second region; a first sidewall insulation filmforming step of forming first sidewall insulation films on sidewalls ofthe gate electrodes; a first insulation film forming step of depositinga second insulation film on the semiconductor substrate with the firstsidewall insulation films and then planarizing a surface of the secondinsulation film; a third insulation film forming step of forming a thirdinsulation film having etching characteristics different from those ofthe second insulation film on the planarized second insulation film; athrough-hole forming step of patterning the second insulation film andthe third insulation film to open first through-holes to be opened onthe first diffused layers, second through-holes to be opened on thesecond diffused layers, and third through-holes to be opened on thefirst diffused layers or the second diffused layers of the peripheralcircuit transistors, or the second gate electrodes; a second conductingfilm depositing step of depositing a second conducting film having thethrough-holes formed in on the semiconductor substrate; a buriedconductor forming step of polishing a surface of the second conductingfilm until the third insulation film is exposed on a surface to formfirst buried conductors buried in the first through-holes, second buriedconductors buried in the second through-holes and third buriedconductors buried in the third through-holes; a third insulation filmforming step of forming a fourth insulation film with fourththrough-holes opened on the first buried conductors, fifth through-holesopened on the second buried conductors and sixth holes opened on thethird buried conductors; a third conducting film depositing step ofdepositing a third conducting film on the semiconductor substrate withthe fourth insulation film formed; and a conducting film removing stepof removing the third conducting film on the fourth insulation film,leaving the second conducting film in the fourth through-holes, thefifth through-holes and the sixth through-holes to form capacitorstorage electrodes of the third conducting film in the fourththrough-holes, first contact conducting film of the third conductingfilm formed in the fifth through-holes and second contact conductingfilm of the third conducting film formed in the sixth contact holes.This method can secure good contact characteristics at the bottoms ofthe through-holes even in the case that the through-holes have higheraspect ratios with higher device integration.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that in the conducting film removing step, asurface of the semiconductor substrate is polished to remove the thirdconducting film on a surface of the fourth insulation film. This methodcan form the buried conductors simultaneously with planarization of theinsulation film.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that the first sidewall insulation films andthe first insulation film function as an etching stopper for forming thethrough-holes; and the through-holes are formed by self-alignment withthe first insulation film and the first sidewall insulation films. Thismethod can easily expose the first diffused layers and the seconddiffused layers on the bottoms of the through-holes.

The above-described objects can be achieved also by a method forfabricating a semiconductor storage device comprising: a gate electrodeforming step of depositing and patterning a first conducting film on asemiconductor substrate to form gate electrodes of the first conductingfilm; a diffused layer forming step of doping the semiconductorsubstrate with an impurity with the gate electrodes as a mask to formfirst diffused layers and second diffused layers; a first insulationfilm forming step of forming a first insulation film having firstthrough-holes and second through-holes formed in, the firstthrough-holes opened on the first diffused layers and the secondthrough-holes opened on the second diffused layers; an opening formingstep of forming openings in the first insulation film, surrounding thefirst through-holes, the opening having a larger diameter than the firstthrough-holes and not reaching the semiconductor substrate; a secondconducting film depositing step of depositing a second conducting filmon the semiconductor substrate having the first insulation film formedon; a conducting film removing step of removing the second conductingfilm on the first insulation film, leaving the second conducting film inthe second through-holes and the openings to form capacitor storageelectrodes of the second conducting film formed in the openings andfirst contact conducting film of the second conducting film formed inthe second through-holes; and a capacitor opposed electrodes formingstep of depositing a second insulation film to be capacitor dielectricfilms and a third conducting film to be capacitor opposed electrodes onthe semiconductor substrate with the capacitor storage electrodes andthe first contact conducting film formed on and then patterning thethird conducting film to form the capacitor opposed electrodes. Thismethod can space the gate electrodes and the through-holes from eachother, whereby short-circuit between the bit lines and the word linesdue to dust, etc. generated in the fabrication steps can be precluded.The openings for forming the capacitor are provided in addition to thesmall-diameter through-holes, which prevent capacitance decrease.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that the method further comprises: after thefirst insulation film forming step, a fourth conducting film depositingstep of depositing a fourth conducting film to fill the firstthrough-holes and the second through-holes, in the openings forming stepthe openings being formed leaving columnar conductors of the fourthconducting film buried in the first through-holes in the openings in aprojecting state. This method can prevent the semiconductor substrateexposed in the first through-holes in forming the openings from beingdamaged. The capacitor dielectric films are formed surrounding thecolumnar conductors, which increases capacitances.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that in the first insulation film forming stepthe first through-holes and the second through-holes are simultaneouslyformed.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that in the first insulation film forming step,the first insulation film is formed of a laminated film of two or morethan two layers having etching characteristics different from eachother; in the opening forming step, the openings are opened to aninterface between the laminated film having different etchingcharacteristics from each other. This method can control a depth of theopenings with good reproducibility, which decreases deviations of thecapacitance.

The above-described objects can be achieved also by a method forfabricating a semiconductor storage device comprising: a gate electrodeforming step of depositing and patterning a first conducting film on asemiconductor substrate to form gate electrodes of the first conductingfilm; a diffused layer forming step of doping the semiconductorsubstrate with an impurity with the gate electrodes as a mask to formfirst diffused layers and second diffused layers; a first insulationfilm forming step of forming a first insulation film with firstthrough-holes and second through-holes formed in, the firstthrough-holes being opened on the first diffused layers and the secondthrough-holes being opened on the second diffused layers; a secondconducting film depositing step of depositing a second conducting filmon the semiconductor substrate having the first insulation film formedon; a second conducting film patterning step of patterning the secondconducting film to form bit lines connected to the second diffusedlayers through the first through-holes and buried conductors buried inthe second-through-holes; and a capacitor forming step of formingcapacitors including capacitor storage electrodes connected to the firstdiffused layers through the buried conductors, capacitor dielectricfilms covering the capacitor storage electrodes and capacitor opposedelectrodes covering at least a part of the capacitor dielectric films.This method can connect the capacitor storage electrodes with the firstdiffused layers through the buried conductors buried at the same timethat the bit lines have been formed, in the second through-holes formedconcurrently with formation of the first through-holes for contact withthe bit lines. Accordingly, the etching time for forming thethrough-holes for contact with the capacitor storage electrodes can bedecreased without addition of a new step, whereby the insulation film onthe bit lines is kept, in the etching, from being etched and exposed.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that the method further comprises: after thesecond conducting film depositing step, a second insulation filmdepositing step of depositing a second insulation film on the secondconducting film; after the second conducting film patterning step, asidewall insulation film forming step of forming sidewall insulationfilms on sidewalls of the bit lines,in the second conducting filmpatterning step, the second insulation film and the second conductingfilm are processed in the same pattern. In this method, simultaneouslytherewith the buried conductors are exposed on the surface. Accordingly,it is unnecessary to form the through-holes for contact with thecapacitor storage electrodes, using a masking step. That is, one maskingstep can be omitted.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that the method further comprises: after thesecond conducting film patterning step, a second insulation film formingstep of forming a second insulation film with openings formed on theburied conductors, wherein in the capacitor forming step, the capacitorstorage electrodes are selectively formed in sidewalls and bottoms ofthe openings. The design rule of the wiring layers formed above can bedesigned with precision.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that the first insulation film forming step ischaracterized by including: a first insulation film depositing step ofdepositing a first insulation film on the semiconductor substrate; anetching stopper film forming step of forming an etching stopper filmwith openings in a region for the first through-holes to be formed inand a region for the second through-holes to be formed in and havingetching characteristics different from those of the first insulationfilm; a sidewall forming step of forming sidewalls having etchingcharacteristics different from those of the first insulation film onsidewalls of the etching stopper film; and a through-hole opening stepof etching the first insulation film with the etching stopper film andthe sidewalls as a mask etching the first insulation film to form thefirst insulation film with the first through-holes and the secondthrough-holes formed in. This method permits the through-holes to havean opening diameter below a resolution limit of an exposing device.

In the above-described method for fabricating a semiconductor storagedevice, it is preferable that in the first insulation film forming step,the first insulation film is deposited on the semiconductor film andthen etching the first insulation film by electron beam lithography witha patterned photo-resist as a mask to open the first through-holes andthe second through-holes. This method permits the first through-holesand the second through holes to have an opening diameter of below aresolution limit of the usual exposing device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of the semiconductor storage device according to afirst embodiment of the present invention explaining a structurethereof.

FIG. 2 is a diagrammatic sectional view of the semiconductor storagedevice according to the first embodiment explaining the structurethereof.

FIGS. 3A-3D are sectional views of the semiconductor storage deviceaccording to the first embodiment in steps of a method for fabricatingthe semiconductor storage device (Part 1).

FIGS. 4A and 4B are sectional views of the semiconductor storage deviceaccording to the first embodiment in steps of a method for fabricatingthe semiconductor storage device (Part 2).

FIGS. 5A and 5B are sectional views of the semiconductor storage deviceaccording to the first embodiment in steps of a method for fabricatingthe semiconductor storage device (Part 3).

FIG. 6 is a sectional view of the semiconductor storage device accordingto the first embodiment in steps of a method for fabricating thesemiconductor storage device (Part 4).

FIG. 7 is a diagrammatic sectional view of the semiconductor storagedevice according to one variation of the first embodiment of the presentinvention explaining a structure thereof.

FIG. 8 is a plan view of the semiconductor storage device according to asecond embodiment of the present invention explaining a structurethereof.

FIG. 9 is a diagrammatic sectional view of the semiconductor storagedevice according to the second embodiment of the present inventionexplaining the structure thereof.

FIGS. 10-10D are sectional views of the semiconductor storage deviceaccording to the second embodiment in steps of a method for fabricatingthe semiconductor storage device (Part 1).

FIGS. 11A and 11B are sectional views of the semiconductor storagedevice according to the second embodiment in steps of a method forfabricating the semiconductor storage device (Part 2).

FIGS. 12A and 12B are sectional views of the semiconductor storagedevice according to the second embodiment in steps of a method forfabricating the semiconductor storage device (Part 3).

FIGS. 13A and 13B are sectional views of the semiconductor storagedevice according to the second embodiment in steps of a method forfabricating the semiconductor storage device (Part 4).

FIGS. 14A and 14B are diagrammatic sectional views of the semiconductorstorage device according to one variation of the second embodiment ofthe present invention explaining a structure thereof.

FIG. 15 is a diagrammatic sectional view of the semiconductor storagedevice according to a third embodiment of the present inventionexplaining the structure thereof.

FIGS. 16A-16C are sectional views of the semiconductor storage deviceaccording to the third embodiment in steps of a method for fabricatingthe semiconductor storage device (Part 1).

FIGS. 17A and 17B are sectional views of the semiconductor storagedevice according to the third embodiment in steps of a method forfabricating the semiconductor storage device (Part 2).

FIGS. 18A and 18B are sectional views of the semiconductor storagedevice according to the third embodiment in steps of a method forfabricating the semiconductor storage device (Part 3).

FIG. 19 is a diagrammatic sectional view of the semiconductor storagedevice according to a fourth embodiment of the present inventionexplaining a method for fabricating the semiconductor storage device.

FIGS. 20A-20C are sectional views of the semiconductor storage deviceaccording to the fourth embodiment in steps of a method for fabricatingthe semiconductor storage device (Part 1).

FIGS. 21A and 21B are sectional views of the semiconductor storagedevice according to the fourth embodiment in steps of a method forfabricating the semiconductor storage device (Part 2).

FIG. 22 is a diagrammatic sectional view of the semiconductor storagedevice according to a fifth embodiment of the present inventionexplaining a method for fabricating the semiconductor storage device.

FIGS. 23A-23C are sectional views of the semiconductor storage deviceaccording to the fifth embodiment in steps of a method for fabricatingthe semiconductor storage device (Part 1).

FIGS. 24A and 24B are sectional views of the semiconductor storagedevice according to the fifth embodiment in steps of a method forfabricating the semiconductor storage device (Part 2).

FIG. 25 is a diagrammatic sectional view of the semiconductor storagedevice according to a sixth embodiment of the present inventionexplaining a method for fabricating the semiconductor storage device.

FIGS. 26A and 26B are sectional views of the semiconductor storagedevice according to the sixth embodiment in steps of a method forfabricating the semiconductor storage device (Part 1).

FIGS. 27A and 27B are sectional views of the semiconductor storagedevice according to the sixth embodiment in steps of a method forfabricating the semiconductor storage device (Part 2).

FIGS. 28A and 28B are sectional views of the semiconductor storagedevice according to the sixth embodiment in steps of a method forfabricating the semiconductor storage device (Part 3).

FIG. 29 is a diagrammatic sectional view of the semiconductor storagedevice according to a seventh embodiment of the present inventionexplaining a method for fabricating the semiconductor storage device.

FIGS. 30A and 30B are sectional views of the semiconductor storagedevice according to the seventh embodiment in steps of a method forfabricating the semiconductor storage device (Part 1).

FIGS. 31A and 31B are sectional views of the semiconductor storagedevice according to the seventh embodiment in steps of a method forfabricating the semiconductor storage device (Part 2).

FIGS. 32A-32D are views explaining problems of the method forfabricating a semiconductor storage device according to the firstembodiment.

FIG. 33 is a plan view of the semiconductor storage device according toan eighth embodiment of the present invention explaining a structurethereof.

FIG. 34 is a diagrammatic sectional view of the semiconductor storagedevice according to the eighth embodiment explaining the structurethereof.

FIGS. 35A-35C are sectional views of the semiconductor storage deviceaccording to the eighth embodiment in steps of a method for fabricatingthe semiconductor storage device (Part 1).

FIGS. 36A and 36B are sectional views of the semiconductor storagedevice according to the eighth embodiment in steps of a method forfabricating the semiconductor storage device (Part 2).

FIGS. 37A and 37B are sectional views of the semiconductor storagedevice according to the eighth embodiment in steps of a method forfabricating the semiconductor storage device (Part 3).

FIG. 38 is sectional view of the semiconductor storage device accordingto the eighth embodiment in steps of a method for fabricating thesemiconductor storage device (Part 4).

FIGS. 39A and 39B are sectional views of the semiconductor storagedevice according to a ninth embodiment in steps of a method forfabricating the semiconductor storage device (Part 1).

FIGS. 40A and 40B are sectional views of the semiconductor storagedevice according to the ninth embodiment in steps of a method forfabricating the semiconductor storage device (Part 2).

FIG. 41 is a diagrammatic sectional view of the semiconductor storagedevice according to a tenth embodiment explaining the structure thereof.

FIGS. 42A and 42B are sectional views of the semiconductor storagedevice according to the tenth embodiment in steps of a method forfabricating the semiconductor storage device (Part 1).

FIGS. 43A and 43B are sectional views of the semiconductor storagedevice according to the tenth embodiment in steps of a method forfabricating the semiconductor storage device (Part 2).

FIG. 44 is a diagrammatic sectional view of the semiconductor storagedevice according to an eleventh embodiment explaining the structurethereof.

FIGS. 45A and 45B are sectional views of the semiconductor storagedevice according to the eleventh embodiment in steps of a method forfabricating the semiconductor storage device (Part 1).

FIGS. 46A and 46B are sectional views of the semiconductor storagedevice according to the eleventh embodiment in steps of a method forfabricating the semiconductor storage device (Part 2).

FIG. 47 is sectional views of the semiconductor storage device accordingto the eleventh embodiment in steps of a method for fabricating thesemiconductor storage device (Part 3).

FIG. 48A is a plan view of the semiconductor storage device according toa twelfth embodiment of the present invention explaining a structurethereof.

FIGS. 48B and 48C are partial sectional views of the semiconductorstorage device according to a twelfth embodiment of the presentinvention explaining a structure thereof.

FIG. 49 is a view of an example of a peripheral circuit of thesemiconductor storage device according to the twelfth embodiment.

FIG. 50 is a plan view of the semiconductor storage device according toa thirteenth embodiment of the present invention explaining a structurethereof.

FIG. 51 is a diagrammatic sectional view of the semiconductor storagedevice according to the thirteenth embodiment explaining the structurethereof.

FIGS. 52A-52D are sectional views of the semiconductor storage deviceaccording to the thirteenth embodiment in steps of a method forfabricating the semiconductor storage device (Part 1).

FIGS. 53A and 53B are sectional views of the semiconductor storagedevice according to the thirteenth embodiment in steps of a method forfabricating the semiconductor storage device (Part 2).

FIGS. 54A and 54B are sectional views of the semiconductor storagedevice according to the thirteenth embodiment in steps of a method forfabricating the semiconductor storage device (Part 3).

FIG. 55 is a diagrammatic sectional view of the semiconductor storagedevice according to one variation of the thirteenth embodiment of thepresent invention explaining a structure thereof.

FIG. 56 is a diagrammatic sectional view of the semiconductor storagedevice according to a fourteenth embodiment explaining the structurethereof.

FIGS. 57A and 57B are sectional views of the semiconductor storagedevice according to the fourteenth embodiment in steps of a method forfabricating the semiconductor storage device (Part 1).

FIGS. 58A and 58B are sectional views of the semiconductor storagedevice according to the fourteenth embodiment in steps of a method forfabricating the semiconductor storage device (Part 2).

FIG. 59 is a diagrammatic sectional view of a conventional semiconductorstorage device explaining a structure thereof (Part 1).

FIG. 60 is a diagrammatic sectional view of a conventional semiconductorstorage device explaining a structure thereof (Part 2).

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

The semiconductor storage device and the method for fabricating the sameaccording to a first embodiment of the present invention will beexplained with reference to FIGS. 1 to 7.

FIG. 1 is a plan view of the semiconductor storage device according tothe present embodiment showing the structure of the device. FIG. 2 is adiagrammatic sectional view of the semiconductor storage device of FIG.1 along the line 2—2. FIGS. 3A-3D, 4A-4B, 5A-5B, and 6 are sectionalviews of the semiconductor storage device according to the presentembodiment in the steps of the method for fabricating the same. FIG. 7is a diagrammatic sectional view of the semiconductor storage deviceaccording to a variation of the present embodiment.

First, the structure of the semiconductor storage device according tothe present embodiment will be explained with reference to FIGS. 1 and2.

Device regions 14, 15 are defined on a silicon substrate 10 by a deviceisolation film 12. Source diffused layers 24 and drain diffused layers26 are formed in the device region 14 independent of each other. Gateelectrodes 20 are formed through gate oxide films 16 on parts of thesemiconductor substrate 10 between the source diffused layers 24 and thedrain diffused layers 26. Thus, memory cell transistors comprising thegate electrodes 20, the source diffused layers 24 and the drain diffusedlayers 26 are constituted.

The gate electrodes 20 are arranged perpendicular to the device region14 and constitute word lines which function as gate electrodes of thememory cell transistors of rest plural memory cells.

On the semiconductor substrate 10 with the memory cell transistorsformed thereon, there is formed an inter-layer insulation film 36 withthrough-holes 38 opened on the drain diffused layers 26 andthrough-holes 40 opened on the source diffused layers 24. Insulationfilms 42 are formed on the gate electrodes 20 by self-alignment,covering the gate electrodes 20. The through-holes 38, 40 are formed byself-alignment with respect to the insulation films 42.

Capacitor storage electrodes 46 of polycrystalline silicon are formed onthe inside walls of the through-holes 40 and the source-diffused layers24, and are connected to the source diffused layers 24 at the bottoms ofthe through-holes 40. Capacitor dielectric films 48 are formed on theinside surfaces and the upper surfaces of the capacitor storageelectrodes 46. Capacitor opposed electrodes 54 are formed in thethrough-holes 40 with the capacitor storage electrodes 46 and thecapacitor dielectric films 48 formed in, and on the inter-layerinsulation film 36. Capacitors thus comprising the capacitor storageelectrodes 46, the capacitor dielectric films 48 and the capacitoropposed electrodes 54 are constituted.

Contact conducting films 44 of polycrystalline silicon are formed on theinside walls of the through-holes 38 and are connected to bit lines 62which are arranged perpendicular to word lines through the inter-layerinsulation film 53 formed on the capacitor opposed electrodes 54.

Wiring layers 70 are formed above the bit lines 62 through aninter-layer insulation film 64, and a DRAM comprising one-transistor andone-capacitor memory cells is constituted.

On the other hand, in the device region 15 for peripheral circuit regionneighboring the memory cell region there are formed source diffusedlayers (not shown) and drain diffused layers 34 independent of eachother. Gate electrodes 22 are formed through gate oxide films 16 onparts of the semiconductor substrate 10 between the source diffusedlayers and the drain diffused layers 34. Thus, peripheral devicetransistors comprising the gate electrodes 22, the source diffusedlayers and the drain diffused layers 34 are constituted.

Through-holes 60 are formed in the inter-layer insulation film 36 on thedrain diffused layers 34 and is connected to wiring layers 70 formed onthe inter-layer insulation film 64 through wiring layers 68 buried inthe through-holes 60.

Then, the method for fabricating the semiconductor storage deviceaccording to the present embodiment will be explained.

The device isolation film 12 is formed in an about 300 nm-thickness onthe major surface of a p-silicon substrate 10 by, e.g., the usual LOCOSto define the device regions 14, 15. Then, gate oxide films 16 areformed in an about 10 nm-thickness on the device region 14, 15 bythermal oxidation (FIG. 3A).

Subsequently, an about 150 nm-thick polycrystalline silicon filmcontaining a high concentration of phosphorus (P), and an about 200nm-thick silicon nitride film are successively formed. Then, the siliconnitride film and the polycrystalline silicon film are concurrentlypatterned by the usual lithography and the etching.

Thus, the gate electrodes 20, 22 having the upper surfaces covered withthe silicon nitride films 18 are formed.

Then, with the silicon nitride films 18 and the gate electrodes 20, 22as a mask, the source diffused layers 24 and the drain diffused layers26 of the memory central transistors, and the low-concentration diffusedlayers 28 of the peripheral circuit transistors are formed byimplanting, for example, P ions under the conditions of a 40 keVacceleration energy and a 2×10¹³ ions cm⁻² dose. The low-concentrationdiffused layers 28 are to be n⁻ layers of the LDD (lightly doped drain)structure (FIG. 3B).

Then, an about 100 nm-thick silicon nitride film is formed by CVD andthen is subjected to anisotropic etching by the use of CHF₃/H₂ gas toform by self-alignment the sidewall nitride films 30 of the siliconnitride film on the sidewalls of the patterned silicon nitride films 18and gate electrodes 20, 22. Thus, the sidewalls and the upper surfacesof the gate electrodes 20, 22 are covered with the silicon nitride films18 and the sidewall nitride films 30. The silicon nitride films 18 andthe sidewall nitride films 30 covering the gate electrodes 20, 22 arehereinafter collectively called insulation films 42 for the convenienceof the explanation.

Subsequently, the source diffused layers and the drain diffused layers34 of n-transistors for peripheral circuits are formed by selectivelyimplanting in the n-transistor region for peripheral circuits, forexample, arsenic (As) ions under the conditions of a 40 keV accelerationenergy and a 4×10¹⁵ ions cm⁻² dose. Thus, peripheral circuit transistorshaving the LDD structure are formed (FIG. 3C).

Then, an about 2 μm thick silicon oxide film is deposited by CVD, andthe surface of the silicon oxide film is polished by CMP (ChemicalMechanical Polishing) and planarized. A polishing amount which canremove a step between the gate electrodes 20, 22 and the deviceisolation film 12 are sufficient. In the present embodiment, thepolishing amount is 500 nm.

The surface may be planarized by depositing a laminated film of asilicon oxide film and a BPSG film in place of the silicon oxide filmand reflowing the BPSG film, but CMP is more preferable in view of theglobal planarization.

Then, a photoresist is patterned by the usual lithography, and then thesilicon oxide film is etched by the use of an etching gas, such as C₂F₆or others. Then, the photoresist is removed to form an inter-layerinsulation film 36 in which are formed the through-holes 38 opened onthe drain diffused layers 26 of the memory cell transistors and thethrough-holes 40 opened on the source diffused layers 24 of the memorycell transistors (FIG. 3D).

In this etching, selectivity of the etching must be sufficiently securedbetween the silicon oxide film and the silicon nitride film to stop theetching of the inter-layer insulation film 36 at the insulation film 42.

The drain diffused layers 26 and the source diffused layer 24 areexposed on the bottoms of the thus-formed through-holes 38, 40. Theregions where the drain diffused layers 26 and the source diffusedlayers 24 are to be exposed are formed by self-alignment with theinsulation film 42. It is not necessary to take into consideration analignment allowance for aligning the through-holes 38, 40 with the gateelectrodes 20 in the lithography. Accordingly, a memory cell area can bedecreased by the alignment allowance.

The depth of the through-holes 40 is an important parameter fordetermining the cell capacitance. In the present embodiment, a depth ofthe through-holes 40 is about 1.5 μm. When a size of the opening of thethrough-holes 40 is 0.3×0.6 μm for example, a sum of a bottom areas ofthe through-holes 40 and a sidewall area thereof is[0.3×0.6+1.5×(0.3+0.6)×2] μm², i.e., about 2.88 μm² can be secured.Accordingly, by forming the capacitor dielectric film of a 4.5 nmthickness in terms of an oxide film, a sufficient capacitor of an about22 fF capacity can be formed.

Subsequently, a polycrystalline silicon film containing a high Pconcentration is formed in an about 50 nm thickness by CVD, and then thepolycrystalline silicon film on the inter-layer insulation film 36 iscompletely removed by CMP, whereby the contact conducting films 44 andthe capacitor storage electrodes 46 are formed by self-alignmentrespectively in the through-holes 38 and in the through-holes 40 (FIG.4A).

The deposition of the inter-layer insulation film 36 is not immediatelyfollowed by the planarization by CMP but may be planarized collectivelytogether with the contact conducting films 44 and the capacitor storageelectrodes 46 concurrently with the formation thereof, whereby one stepof the polishing by CMP can be decreased.

The capacitor storage electrode 46 and the contact conducting film 44may be formed of polycrystalline silicon film whose surface iscorrugated (e.g., H. Watanabe, Ext. Abstract of 22nd SSDM, p.869(1990)), whereby a surface area of the capacitor storage electrode 46 isincreased about twice a surface area formed by the usual method. Even ina case where a depth of the through-holes 40 is as shallow as about ahalf a depth of the through-holes 40, about 0.8 μm, the same capacitancecan be secured.

Next, a silicon nitride film of an about 5 nm-thickness is formed byCVD, and then the surface of the silicon nitride film is oxidized in awet atmosphere of 800° C. to form the capacitor dielectric film 48 of anabout 4.5 nm-thickness in terms of an oxide film.

Then, the polycrystalline silicon film 50 of an about 150 nm-thicknesscontaining a high concentration of P, and a BPSG film 52 of an about 200nm-thickness is successively formed, and then the surface of the BPSGfilm 52 is planarized by reflow or CMP. At this time, the through-holes38 are completely filled with the polycrystalline silicon film 50 (FIG.4B).

Subsequently, the BPSG film 52 and the polycrystalline silicon film 50are patterned together by the usual lithography step and etching step toform the capacitor opposed electrodes 54.

Then, an about 100 nm-thick silicon oxide film is deposited by CVD, andthe entire surface is subjected to anisotropic etching to form thesidewall oxide films 56 on the sidewalls of the capacitor opposedelectrodes 46, and to remove the capacitor dielectric film 48 on thethrough-holes 38.

Thus, the capacitor opposed electrodes 54 are covered with theinter-layer insulation film 53 constituted by the sidewall oxide films56 and the BPSG films, and the openings formed on the through-holes 38can be used as the bit line contact holes 58. That is, the sidewalloxide films 48 are formed while the bit line contact holes 58 can beformed by self-alignment (FIG. 5A).

Then, the contact holes 59 for the capacitor opposed electrodes 54, andthe through-holes 60 for the peripheral circuit transistors, etc. areopened by the usual lithography step and etching step (FIG. 5B).

Subsequently, an about 50 nm-thick titanium (Ti) film, and an about 50nm-thick TiN film and an about 200 nm-thick tungsten (W) film aresuccessively formed respectively by collimated sputtering and by CVD.Then, the laminated film of the W/TiN/Ti film is patterned by the usuallithography step and etching step to form the bit lines 62 and thewiring layers 68.

Then, the inter-layer insulation film 64 of an about 1 μm-thick siliconoxide film is deposited by CVD, and the surface of the inter-layerinsulation film 64 is planarized by CMP or others as required. Then, viaholes 66 are opened.

Then, a W film is deposited by CVD and patterned to form the wiringlayers 70. The wiring layers 70 may be of aluminium (Al) deposited bysputtering.

Thus, a DRAM comprising one-transistor and one-capacitor memory cells isformed (FIG. 6).

As described above, according to the present embodiment, lithographysteps which require precise patterning are totally 8 for defining thedevice isolation region, formation of the gate electrodes, opening thethrough-holes for the capacitor storage electrodes and the bit linecontact through-holes, formation of the capacitor opposed electrodes,opening the peripheral circuit through-holes, and formation of the bitlines, the via holes, and the wiring layers. In comparison with theconventional example of FIG. 60, lithography steps can be decreased byone step.

In comparison with the conventional example of FIG. 59, the presentembodiment has the same number of lithography steps as the example, butthe formation of the through-holes for the capacitor storage electrodesand the bit line contact through-holes by self-alignment with the gateelectrodes can decrease alignment allowances.

The formation of the bit line contact through-holes and thethrough-holes for the capacitor storage electrodes by self-alignmentwith the insulation films formed around the gate electrodes byself-alignment makes alignment allowances unnecessary, which makesmemory cell areas accordingly smaller.

The capacitor storage electrodes and the bit line contact conductingfilms are formed at the same time, but the wiring layers buried in theperipheral circuit through-holes and the capacitor storage electrode areformed separately from each other, whereby capacities of the capacitorare not substantially sacrificed.

In the peripheral circuit region of the present embodiment, the wiringlayers 70 in the via holes 66 are formed through the wiring layers 68 inthe through-holes 60. To this end another lithography step is necessaryto form the peripheral through-holes 60, but the structure of FIG. 7permits this lithography step to be omitted.

In this case, after the through-holes 59 for the capacitor opposedelectrodes 54, the peripheral circuit through-holes 60 are opened afterthe inter-layer insulation film 64 is formed, and the wiring layers 70are directly in contact with the capacitor opposed electrodes 54 and thesource-drain diffused layers 34 of the peripheral circuit transistors.

Second Embodiment

The semiconductor storage device according to a second embodiment of thepresent invention, and the method for fabricating the same will beexplained with reference to FIGS. 8 to 14. Common members of thesemiconductor storage device and the method for fabricating the sameaccording to the present embodiment with those of the first embodimentare represented by common reference numerals to simplify or not torepeat their explanation.

FIG. 8 is a plan view of the semiconductor storage device according tothe present embodiment. FIG. 9 is a diagrammatic sectional view of thesemiconductor storage device of FIG. 8 along the line 9—9. FIGS.10A-10D, 11A-11B, 12A-12B, and 13A-13B are sectional views of thesemiconductor storage device according to the present embodiment in thesteps of the method for fabricating the same, which explain thefabrication method. FIG. 14 is sectional views of one variation of thesemiconductor storage device in steps of the method for fabricating thesame, which explain the fabrication method.

The semiconductor storage device according to the variation of the firstembodiment shown in FIG. 7 simplifies the fabrication steps by buryingthe peripheral circuit through-holes 60 by the wiring layers 70. A depthof the through-holes 60 sometimes is even about 3 μm, and in such caseit is difficult to completely bury the through-holes.

Taking this into consideration, the semiconductor storage device and themethod for fabricating the same according to the present embodiment cansimplify the fabrication steps.

First, the structure of the semiconductor storage device according tothe present embodiment will be explained.

Device regions 14, 15 are defined on a silicon substrate 10 by a deviceisolation film 12. In the device regions 14 there are formed sourcediffused layers 24 and drain diffused layers 26 independent of eachother. Gate electrodes 20 are formed through gate oxide films 16 onparts of the semiconductor substrate 10 between the source diffusedlayers 24 and the drain diffused layers 26. Thus, memory celltransistors comprising the gate electrodes 20, the source diffusedlayers 24 and the drain diffused layers 26 are constituted.

On the semiconductor substrate 10 with the memory cell transistorsformed thereon, there is formed inter-layer insulation film 36 withthrough-holes 38 and through-holes 40 opened respectively on the draindiffused layers 26 and the source diffused layers 24. Insulation films42 are formed on the gate electrodes 20, covering the same. Thethrough-holes 38 and the through-holes 40 are opened by self-alignmentwith the insulation films 42.

Capacitor storage electrodes 46 of polycrystalline silicon are formed onthe inside walls of the through-holes 40 and the source diffused layers24 and connected to the source diffused layers 24 at the bottoms of thethrough-holes 40. Capacitor dielectric films 48 are formed on the insidesurfaces and the top surfaces of the capacitor storage electrodes 46.Capacitor opposed electrodes 54 are formed in the through-holes 40 withthe capacitor storage electrodes 46 and the capacitor dielectric films48 formed in, and on the inter-layer insulation film 36. Capacitors areconstituted by the capacitor storage electrodes 46, the capacitordielectric films 48 and the capacitor opposed electrodes 54.

Contact conducting films 44 of polycrystalline silicon are formed on theinside walls of the through-holes 38 and connected to bit lines 62arranged normal to word lines through the inter-layer insulation film 53formed on the capacitor opposed electrodes 54.

Wiring layers 70 are formed above the bit lines 62 through aninter-layer insulation film 64. Thus, a DRAM comprising one-transistorand 1-capacitor memory cells is constituted.

On the other hand, in the peripheral circuit region neighboring thedevice region 15 there are formed source diffused layers (not shown) anddrain diffused layers 34 independent of each other. Gate electrodes 22are formed on parts of the semiconductor substrate 10 between the sourcediffused layers and the drain diffused layers 34 through gate oxidefilms 16. Thus, peripheral circuit transistors are constituted by thegate electrodes 22, the source diffused layers and the drain diffusedlayers 34 are constituted.

Through-holes 60 are formed in inter-insulation films 36 formed on thedrain diffused layers 34 and are connected to wiring layers 70 on aninter-layer insulation film 64 through a wiring layer 68 buried in thethrough-holes 60.

A difference of the semiconductor storage device according to thepresent embodiment from that according to the first embodiment is that,in the present embodiment, the polycrystalline silicon films 50 formingthe capacitor opposed electrodes 54, and the inter-layer insulation film53 on the capacitor opposed electrode 54 are extended to the peripheralcircuit region.

A merit of forming the capacitor opposed electrodes 54 and theinter-layer insulation film 53 in such arrangement is primarily tosimplify the fabrication process. Next, the method for fabricating thesemiconductor storage device according to the present embodiment will beexplained, and this arrangement will be detailed.

A device isolation film 12 of an about 300 nm-thickness are formed onthe major surface of a p-silicon substrate 10 by, e.g., the usual LOCOSto define the device regions 14, 15. Then, the gate oxide films 16 of anabout 10 nm-thickness are formed in the device regions 14, 15 by thermaloxidation (FIG. 10A).

Subsequently, a polycrystalline silicon film containing a highconcentration of P and a silicon nitride film are successively formed byCVD respectively in an about 150 nm-thickness and an about 200nm-thickness. Then, the silicon nitride film and the polycrystallinesilicon film are concurrently patterned by the usual lithography. Thus,the gate electrodes 20, 22 having top surfaces covered with the siliconnitride films 18 are formed.

Then, with the silicon nitride films 18 and the gate electrodes 20, 22as a mask, the source diffused layers 24 and the drain diffused layers26 of the memory cell transistors, and the low-concentration diffusedlayers 28 of the peripheral circuit transistors are formed byimplanting, for example, P ions under the conditions of a 40 keVacceleration energy and a 2×10 ¹³ ions cm⁻² dose (FIG. 10B).

Subsequently, an about 100 nm-thick silicon nitride film is formed byCVD and subjected to anisotropic etching by the use of CHF₃/H₂ gas, andthe sidewall nitride films 30 are formed by self-alignment on thesidewalls of the patterned silicon nitride films 18 and gate electrodes20, 22. Thus, the top surfaces and the sidewalls of the gate electrodes20, 22 are covered with the silicon nitride films 18 and the sidewallnitride films 30.

Subsequently, As ions, for example, are selectively implanted in theperipheral circuit n-transistor region, by the usual lithography, underthe conditions of a 40 keV acceleration energy and a 4×10¹⁵ ions cm⁻² toform the source diffused layers and the drain diffused layers 34 of theperipheral circuit n-transistors. Thus, peripheral circuit transistorsof the LDD structure are formed (FIG. 10C).

Then, silicon oxide film is deposited in an about 2 μm-thickness by CVDand the surface of the silicon oxide film is polished by CMP forplanarization. An amount polished by the CMP which removes a stepbetween the gate electrodes 20, 22 and the device isolation film 12 issufficient, and is 500 nm in the present embodiment.

Then, after a photoresist is patterned by the usual lithography, thesilicon oxide film is etched, using an etching gas, such as C₂F₆ orothers. Then, the photoresist is removed, and the inter-layer insulationfilm 36 with the through-holes 38 opened on the drain diffused layers 26of the memory cell transistors and the through-holes 40 opened on thesource diffused layers 24 of the memory cell transistors formed in isformed (FIG. 10D).

Subsequently, a polycrystalline silicon film containing a highconcentration of P is formed in an about 50 nm thickness by CVD, andparts of the polycrystalline silicon film on the inter-layer insulationfilm 36 are completely removed. Thus, the contact conducting films 44 inthe through-holes 38, and the capacitor storage electrodes 46 in thethrough-holes 40 are formed self-alignment (FIG. 11A).

Next, an about 5 nm-thick silicon nitride film is formed by CVD and thenthe surface of the silicon nitride film is oxidized in a wet atmosphereof 800° C. to form the capacitor dielectric films 48 of an about 4.5nm-thickness in terms of an oxide film.

Then, an about 150 nm-thick polycrystalline silicon film 50 containing ahigh concentration of P, and an about 200 nm-thick of BPSG film 52 aresuccessively formed, and then the surface of the BPSG film 52 isplanarized by reflow or CMP. At this time, the through-holes 38 arecompletely filled by the polycrystalline silicon film 50 (FIG. 11B).

Subsequently, a photoresist 72 is patterned by the usual lithography,using a positive photoresist, and then the BPSG film 52 and thepolycrystalline silicon film 50 are successively etched to formed thecapacitor opposed electrodes 54. At this time, the polycrystallinesilicon film 50 and the BPSG film 52 in the peripheral circuit regionare opened down to the top of the capacitor dielectric films 48 only inthe regions with the peripheral circuit through-holes 60 formed in (FIG.12A).

Then, with the photoresist 72 left, a photoresist is patterned by theuse of a negative-photoresist to form a photoresist 74 for covering thememory cell region. In patterning of the photoresist 74, precisealignment is not necessary as long as the memory cell region can becovered, which drastically simplifies the lithography step.

The photoresist 74 is formed by the use of a negative photoresist forthe prevention of an inconvenience that the lower photoresist 72 ispeeled together. Accordingly, it is possible to cure the photoresist 72by, e.g., UV immediately after the photoresist 72 is patterned, and thenthe patterning is conducted by the use of a positive resist.

Subsequently, etching is conducted with the photoresists 72, 74 as amask to completely open the through-holes 60 in the peripheral circuits(FIG. 12B).

After the photoresists 72, 74 have been removed, an about 100 nm-thicksilicon oxide film is deposited, and the entire surface is subjectedanisotropic etching, whereby the sidewall oxide films 56 are formed onthe sidewalls of the capacitor opposed electrodes 46, and the sidewalloxide films 76 are formed on the inside walls of the through-holes 60.Simultaneously therewith the capacitor dielectric films 48 on thethrough-holes 38 are removed.

Thus, the capacitor opposed electrodes 54 are covered with theinter-layer insulation film 53 formed of the sidewall oxide films 56 andthe BPSG films, so that the openings formed on the through-holes 38 canbe used as the bit line contact holes 58. That is, the sidewall oxidefilms 56 are formed, and at the same time the bit line contact holes 58are formed by self-alignment (FIG. 13A).

Then, successively an about 50 nm-thick Ti film is formed by collimatedsputtering, and an about 50 nm-thick TiN film and an about 200 nm-thickW film are formed by CVD. Then, a laminated film of the W/TiN/Ti film ispatterned to form the bit lines 62 and the wiring layer 68.

Then, the inter-layer insulation film 64 of an about 1 μm thick siliconoxide film is deposited by CVD, and the surface of the inter-layerinsulation film 64 is planarized by CMP or other technique as required.Then, via holes 66 are opened.

Subsequently, a W film is deposited CVD and then patterned to form thewiring layers 70.

Thus, a DRAM comprising 1-transistor and 1-capacitor memory cells isformed (FIG. 13B).

As described above, according to the present embodiment, lithographysteps necessary to form precise patterns in fabricating thesemiconductor storage device are 7 steps for defining the deviceisolation region, forming the gate electrodes, opening the through-holesfor the capacitor storage electrodes and the through-holes for the bitline contact, and forming the capacitor opposed electrodes, the bitlines, the via holes and the wiring layers. The lithography stepsimplified by the present embodiment is for opening the through-holes inthe peripheral circuit region. In comparison with the conventionalexample of FIG. 60, the present embodiment can decrease lithographysteps by one step and can simplify one lithography step.

In comparison with the conventional example of FIG. 59, as in the firstembodiment, the alignment allowance between the through-holes for thecapacitor storage electrodes and the through-holes for the bit linecontact with the gate electrodes can be smaller.

In the above-described embodiment, in opening the through-holes in theperipheral circuit region, the photoresist 72 is formed; thethrough-holes are opened down to the top surface of the capacitordielectric films 48, and then the photoresist 74 is formed withoutremoving the photoresist 72; and the through-holes 60 are completelyopened, the through-holes 60 may be opened by the following fabricationmethod.

A BPSG film is deposited as shown in FIG. 11B and then an about 100nm-thick polycrystalline silicon film 78 is deposited by CVD.

Then, a photoresist 72 is patterned by the usual lithography, and nextthe polycrystalline silicon film 78, the BPSG film 52 and thepolycrystalline silicon film 50 are successively etched to form thecapacitance-opposed electrodes 54. At this time, without removing thepolycrystalline silicon film 50 and the BPSG film 52 in the peripheralcircuit region, the polycrystalline silicon film 50 is opened down tothe capacitor dielectric films 48 only in the regions of the peripheralcircuit region for the through-holes 60 to be formed in (FIG. 14A).

After the photoresist 72 is removed, the photoresist 74 is againpatterned by the usual lithography to cover the memory cell region witha photoresist 74.

Subsequently, with the photoresist 74 as a mask, the capacitancedielectric film 48 and the inter-layer insulation film 36 are etched tocompletely open the through-holes 60. At this time, the inter-layerinsulation film 53 is not etched in etching the through-holes 60 becauseof the polycrystalline silicon film 78 formed on the inter-layerinsulation film 53. Thus, no subtle alignment precision is unnecessaryin patterning the photoresist 74, which simplifies the lithography step(FIG. 14B).

The polycrystalline silicon film 78 remains after the through-holes 74have been opened but causes no trouble if patterned together with thebit lines 62 formed thereon.

Third Embodiment

The semiconductor storage device according to a third embodiment of thepresent invention and the method for fabricating the same will beexplained with reference to FIGS. 15 to 18. Common members of thesemiconductor storage device and the method for fabricating the sameaccording to the third embodiment with those according to the first andthe second embodiments are represented by common reference numerals tosimplify and not to repeat their explanation.

FIG. 15 is a diagrammatic sectional view of the semiconductor storagedevice according to the present embodiment. FIGS. 16A-16C, 17A-17B, and18A-18B are sectional views of the semiconductor storage deviceaccording to the present embodiment in the steps of the method forfabricating the same, which explain the fabrication method.

The present embodiment uses the same structure the bit line contact andthe contact of the peripheral circuit region, whereby the method forfabricating the semiconductor storage device according to the first andthe second embodiments can be further simplified.

First, the structure of the semiconductor storage device according tothe present embodiment will be explained.

Device regions 14, 15 are defined on a silicon substrate 10 by a deviceisolation film 12. Source diffused layers 24 and the drain diffusedlayers 26 are formed independent of each other in the device region 14.Gate electrodes 20 are formed through gate oxide films 16 on parts ofthe semiconductor substrate 10 between the source diffused layers andthe drain diffused layers 26. Thus, the gate electrodes 20, the sourcediffused layers 24 and the drain diffused layers 26 constitute memorycell transistors.

The gate electrodes 20 constitute word lines which function as gateelectrodes of the memory cell transistors of other plural memory cells.

On the semiconductor substrate 10 with the memory cell transistorsformed on there is formed an inter-layer insulation film 36 withthrough-holes 38 opened on the drain diffused layers 26 andthrough-holes 40 opened on the source diffused layers 24. Insulationfilms 42 is formed on the gate electrodes 20 by self-alignment, coveringthe gate electrodes 20, and the through-holes 38, 40 are formed byself-alignment with the insulation films 42.

Capacitor storage electrodes 46 of TiN film are formed on the insidewalls of the through-holes 40 and on the source diffused layers 24 andare connected to the source diffused layers 24 at the bottoms of thethrough-holes 40. Capacitor dielectric films 48 are formed on the insidewalls and the top surfaces of the capacitor storage electrodes 46.Capacitor opposed electrodes 54 are formed in the through-holes 40 withthe capacitor storage electrodes 46 and the capacitor dielectric films48 formed thereon, and on the inter-layer insulation film 36. Thus, thecapacitor storage electrodes 46, the capacitor dielectric films 48 andthe capacitor opposed electrodes 54 constitute capacitors.

Contact conducting films 44 of TiN film are formed on the inside wallsof the through-holes 38 and are connected, through the inter-layerinsulation film 53 formed on the capacitor opposed electrodes 54, to bitlines 62 arranged normal to word lines.

Wiring layers 70 are formed above the bit lines 62 through inter-layerinsulation film 64. A DRAIM comprising 1-transistor and 1-capacitormemory cells is constituted.

On the other hand, in the device region 15, peripheral circuit regionneighboring the memory cell region, source diffused layers (not shown)and the drain diffused layers 34 are formed independent of each other.Gate electrodes 22 are formed through gate oxide films 16 on parts ofthe semiconductor substrate 10 between the source diffused layers andthe drain diffused layers 34. Thus, peripheral circuit transistorscomprising the gate electrodes 22, the source diffused layers and thedrain diffused layers 34 are constituted.

Through-holes 60 are formed in the inter-layer insulation film 36 on thedrain diffused layers 34, and the gate electrodes 22. Conducting films80 of TiN film are formed on the inside walls and the bottom of thethrough-holes 60, and the drain diffused layers 34 and the gateelectrodes 22 are connected to the wiring layers 68 through theconducting films 80.

Then, the method for fabricating the semiconductor storage deviceaccording to the present embodiment will be explained.

First, a device isolation film 12 of an about 300 nm-thickness areformed on the major surface of a p-silicon substrate by, e.g., the usualLOCOS to define the device regions 14, 15. Then, gate oxide film 16 ofan about 10 nm thickness is formed in the device regions 14, 15 bythermal oxidation.

Subsequently, an about 150 nm-thick polycrystalline silicon filmcontaining a high concentration of P and an about 200 nm-thick siliconnitride film are successively formed by CVD and then part of the siliconnitride film in the peripheral circuit region is removed by the usuallithography. This region is to be a gate contact 82 through which wiringof the gate electrodes 22 are to be led out.

A silicon nitride film and a polycrystalline silicon film areconcurrently patterned by the usual lithography and etching to form thegate electrodes 20 of the memory cell transistors and the gateelectrodes 22 for peripheral circuits.

The top surfaces of the thus-formed gate electrodes 20, 22 are coveredwith the silicon nitride films 18 except the gate contact 82 of theperipheral circuit region.

Then, with the silicon nitride films 18 and the gate electrodes 20, 22as a mask, the source diffused layers 24 and the drain diffused layersof the memory cell transistors, and the low concentration diffusedlayers 28 of the peripheral circuit transistors are formed byimplanting, for example, P ions under the conditions of a 40 keVacceleration energy and a 2×10¹³ ions cm⁻² dose. The low concentrationdiffused layers 28 are to be n⁻ layers of LDD structure (FIG. 16A).

Next, an about 100 nm-thick silicon nitride film is formed and then issubjected to anisotropic etching using CHF₃/H₂ gas to form byself-alignment sidewall nitride films 30 of the silicon nitride film onthe sidewalls of the patterned silicon nitride films 18 and gateelectrodes 20, 22, whereby the sidewalls and the top surfaces of thegate electrodes 20, 22 are covered with the silicon nitride films 18 andthe sidewall nitride films 30. Hereinafter the silicon nitride films 18and the sidewall nitride films 30 covering the gate electrodes 20, 22will be collectively called an insulation film 42 for the convenience ofexplanation.

Subsequently, source diffused layers 32 and drain diffused layers 34 ofthe peripheral circuit n-transistors are formed by selectivelyimplanting, by the usual lithography, in the peripheral circuitn-transistors, for example, As ions under the conditions of a 40 kevacceleration energy and a 4×10¹⁵ ions cm⁻² dose. Thus, peripheralcircuit transistors having an LDD structure are constituted (FIG. 16B).

Subsequently, a silicon oxide film is deposited in an about 2.5 μm byCVD, and the surface of the silicon oxide film is polished about 0.5 μmby CMP for planarization.

In place of the 2,5 μm-thick silicon oxide film, for example, alaminated film of a 50 nm-thick silicon oxide film and a 2 μm-thick BPSGfilm are deposited, and the surface of the laminated film may beplanarized by reflowing the BPSG films for about 15 minutes at 850° C.in a nitrogen atmosphere.

Then, a photoresist is patterned by the usual lithography, and then thesilicon oxide film is etched with an etching gas, such as C₂F₆ orothers.

Next, the photoresist is removed, and inter-layer insulation film 36with the through-holes 38 opened on the drain diffused layers 26 of thememory cell transistors, the through-holes 40 opened on the sourcediffused layers of the memory cell transistors and the through-holes 60of the peripheral circuit region is formed (FIG. 16C).

The drain diffused layers 26 and the source diffused layers 24 areexposed on the bottoms of the thus-formed through-holes 38, 40. Theseexposed regions for the drain diffused layers 26 and the source diffusedlayers 24 exposed on are formed by self-alignment with the insulationfilm 42. Accordingly, no alignment allowance for the alignment with thegate electrodes 20 is necessary in patterning the through-holes 38, 40.A memory cell area can be accordingly reduced by an alignment allowance.

On the other hand, the gate electrodes 22 and the drain diffused layers34 are exposed on the bottoms of the through-holes 60. The insulationfilms 42 on the gate electrodes 22 have been removed in the gate contact82 for the through-hole 60 to be formed in, so that the through-hole 60can be opened together with the through-holes 38, 40, whereby the gateelectrodes 22 can be exposed in the through-holes 60.

Subsequently, an about 10 nm-thick Ti film and an about 20 nm-thick TiNfilm are successively formed by CVD, and the TiN film and of Ti film onthe inter-layer insulation film 36 are completely removed. Thus, thecontact conducting films 44, the capacitor storage electrodes 46 and theconducting films 80 are formed by self-alignment respectively in thethrough-holes 38, the through-holes 40 and the through-holes 60 in theperipheral circuit region (FIG. 17A).

In forming the conducting films 80, it is possible that the Ti film isdeposited mainly on the bottoms of the through-holes by collimatedsputtering having more vertical sputtering component, and then the TiNfilm is grown by CVD.

In forming the contact conducting films 44, the capacitor storageelectrodes 46 and the conducting films 80, it is possible that thephotoresist is left in the through-holes 38, the through-holes 40 andthe through-holes 60, and with the photoresist as a mask, the Ti filmand the TiN film is etched off by using lithography in place of CMP.

The electric resistance of the conducting films 80 buried in thethrough-holes 60 of the peripheral circuit region is very importantbecause the operation speed of a peripheral circuit depends on theelectric resistance. An electric resistance of the conducting films 80is sufficiently as low as about 75 Ω since a sheet resistance of thethus-formed conducting films 80 is about 30 Ω/□, a depth of thethrough-holes 60 is about 2 μm, and a circumferential edge length of thethrough-holes 60 is about 0.8 μm.

Then, an about 5 nm-thick silicon nitride film is formed by CVD at a lowtemperature of about 650° C. and then is thermally treated for 10minutes in a 4 atmospheric pressure wet atmosphere of 700° C. to oxidethe surface of the silicon nitride film and form the capacitordielectric films 48.

This thermal treatment causes the Ti films of the bottoms of thethrough-holes 38, 40, 60 to have silicidation with the base source/draindiffused layers 24, 26, 32, 34 or the gate electrodes 22, and contactresistances of these connections are decreased.

The thermal treatment for forming the capacitor dielectric films 48used, as described above, high pressure oxidation at the lowtemperature. This is because the high-pressure oxidation, which allowsthe thermal treatment temperature to be low, is preferable because whenthe TiN film reacts with the silicon nitride film in a high-temperaturethermal treatment, there is a risk that the capacitor dielectric films48 may lower its breakdown voltage.

Then, the polycrystalline silicon film 50 containing a highconcentration of P and the silicon oxide film 52 are successively formedby CVD respectively in an about 150 nm thickness and an about 200 nmthickness. Thus, the through-holes 38, 40, 60 are filled.

Subsequently, the silicon oxide film 52 and the polycrystalline siliconfilm 50 are together patterned by the usual lithography and etching toform the capacitor opposed electrodes 54 (FIG. 17B).

The silicon oxide film 52 and the polycrystalline silicon film 50remain, buried in the through-holes 38, 60, but these films contributeonly to planarization without troubles.

A material of the capacitor opposed electrodes 54 may be TiN filmdeposited by CVD, but in the present embodiment polycrystalline siliconfilm 50 is used because the dielectric films may be damaged in growingthe TiN film using a chlorine-based reactive gas.

Then, an about 100 nm-thick silicon oxide film is deposited by CVD, andthe entire surface is subjected to anisotropic etching to form thesidewall oxide films 56 on the sidewalls of the capacitor opposedelectrodes 54, simultaneously removing the capacitor dielectric films 48on the through-holes 38.

Thus, the capacitor opposed electrodes 54 are covered with the sidewalloxide films 56 and the inter-layer insulation film 53, so that theopenings formed on the through-holes 38 can be used as bit line contactholes 58. That is, the bit line contact holes 58 can be self-alignedsimultaneously with formation of the sidewall oxide films 56 (FIG. 18A).

Subsequently, an about 50 nm-thick Ti film is formed by collimatedsputtering, and an about 50 nm-thick TiN film and an about 200 nm-thickW film are formed by CVD. Then, a laminated film of the W/TiN/Ti film ispatterned to form the bit lines 62 and the wiring layers 68.

Next, the inter-layer insulation film 64 of an about 1 μm-thick siliconoxide film is deposited by CVD, and the surface of the film isplanarized by CMP or others as required, and then the via hole 66 isopened.

Subsequently, a W film is deposited by CVD and then patterned to formthe wiring layers 70.

Thus, a DRAM comprising 1-transistor and 1-capacitor memory cells isconstituted (FIG. 18B).

As described above, according to the present embodiment, the conductingfilms buried in the through-holes for connecting the bit lines and thememory cell transistors are formed of a material of low resistance,whereby the through-holes of the peripheral circuit region and those ofthe memory cell region can have the same structure. One lithography stepcan be omitted.

Accordingly, lithography steps which need precise patterning are fordefining the device isolation region, forming the gate electrodes,opening the through-holes, and forming the capacitor opposed electrodes,the bit lines, the via hole, and the wiring layers, totally 7 steps. Incomparison with the conventional example shown in FIG. 60, twolithography steps can be decreased.

In comparison with the conventional example of FIG. 59, one lithographystep can be decreased, and furthermore, in the present embodiment, thethrough-holes for the capacitor storage electrodes and the through-holesfor the bit line contact are formed by self-alignment with the gateelectrodes. This makes it possible to decrease alignment allowances.This also makes it possible to decrease a thickness of the capacitorstorage electrodes, whereby decreases of a capacitance can be prevented.

The semiconductor storage device according to the present embodimentincludes the capacitor storage electrodes formed of TiN film, thecapacitor dielectric film formed of SiN film, and the capacitor opposedelectrodes formed of polycrystalline silicon film. As described,however, in, e.g., K. Koyama (Technical Digest IEDM 1992, p.823 (1992)),H. Shinriki (IEEE Trans., Electron Devices, vol. 38, No.3, p.455(1991)), the capacitor may be constituted by capacitor dielectric filmsof a high and intense dielectric film, such as Ta₂O₅ film,(Ba_(x)Sr_(1−x))TiO₃ film or others, and the capacitor storageelectrodes and the capacitor opposed electrodes may be formed of anelectrode material, such as W or Pt, which are usable for theabove-described dielectric films.

The capacitors are formed of such high and intense dielectric film,whereby sufficient capacitances can be secured even with reduced surfaceareas of the capacitor electrodes. In the case that among the highestdielectric constant one of the above-described materials is used, veryeffectively the through-holes can be shallowed up to about 0.2 μm.

In the above-described embodiment, the capacitor-storage electrodes andthe capacitor opposed electrodes are formed of a laminated film of Tifilm and TiN film but may be formed of any other material as long as itis a conducting film which can sufficiently lower the contactresistance.

Fourth Embodiment

The semiconductor storage device according to a fourth embodiment of thepresent invention and a method for fabricating the same will beexplained with reference to FIGS. 19 to 21. Common members of thepresent embodiment with the semiconductor storage device and the methodfor fabricating the same according to the third embodiment shown inFIGS. 15 to 18 are represented by common reference numerals to simplifyand not repeat their explanation.

FIG. 19 is a diagrammatic sectional view of the semiconductor storagedevice according to the present embodiment, and FIGS. 20A-20C, and21A-21B are sectional views of the semiconductor storage deviceaccording to the present embodiment in the steps of the method forfabricating the same, which explain the method.

In the first to the third embodiments, to open the through-holes 38, 40,etc., the inter-layer insulation film 36 of an about 2 μm-thickness isonce etched. In the actual fabrication process, it is usual to conductoveretching corresponding to a film thickness of the inter-layerinsulation film, taking into consideration disuniformity of the filmthickness upon forming the film. Accordingly, considerable over-etchingis needed to etch the inter-layer insulation film 36 of an about 2μm-thickness.

To open the through-holes 38, 40, the insulation films 42 are used asetching stoppers, whereby the self-aligned contact is formed. Siliconnitride films formed on steps, such as the insulation films 42, havelower etching selectivity with respect to silicon oxide film thansilicon -nitride film formed on plane portions. Etching of theinsulation films 42 tend to accelerate especially on the edges, etc. ofthe gate electrodes 20, 22.

Accordingly, in opening the through-holes 38, 40, etc. in a thickinter-layer insulation film, there is a risk that the insulation films42 are excessively over-etched to expose the gate electrodes 20, 22 witha result, for example, that the contact conducting films to be buried inthe through-holes 38 and the gate electrodes 20 may be short-circuited.

Thus, the formation of the through-hoes 38, 40 is one of the mostdifficult fabrication steps of the method of the present invention.

In the present embodiment, taking into consideration the above-describedproblems, the semiconductor storage device and the method forfabricating the same which make it easy to form the through-holes 38, 40will be explained.

The semiconductor storage device according to the present embodiment ischaracterized in that inter-layer insulation film formed between bitlines 62 and a silicon substrate 40 are an insulation film of athree-layer structure.

That is, inter-layer insulation film 36 constituted by silicon oxidefilms 84, silicon nitride films 86 and silicon oxide films 88sequentially laid one on another are formed on the semiconductorsubstrate 10 with memory cell transistors including gate electrodes 20,source diffused layers 24 and-drain diffused layers 26 formed on.

In the inter-layer insulation film 36, the through-holes 38 opened onthe drain diffused layers 26 and the through-holes 40 opened on thesource diffused layers 24 are formed.

Capacitor storage electrodes 46 of TiN film are formed on the insidewalls of the through-holes 40 and the source diffused layers 24 andconnected to the source diffused layers 24 at the bottoms of thethrough-holes 40. Capacitor dielectric films 48 are formed on the insidesurfaces and the top surfaces of the capacitor storage electrodes 46.Capacitor opposed electrodes 54 are formed in the through-holes 40 withthe capacitor storage electrodes 46 and the capacitor dielectric films48 formed on and on the inter-layer insulation film 36. Thus, capacitorsconstituted by the capacitor storage electrodes 46, the capacitordielectric films 48 and the capacitor opposed electrodes 54.

Contact conducting films 44 are formed on the inside walls of thethrough-holes 38 and connected to bit lines 62 arranged normal to wordlines through an inter-layer insulation film 53 formed on the capacitoropposed electrodes 54.

Wiring layers 70 are formed above the bit lines 62 through aninter-layer insulation film 64. Thus, a DRAM comprising 1-transistor and1-capacitor memory cells is constituted.

Then, the method for fabricating the semiconductor storage deviceaccording to the present embodiment will be explained.

First, an about 300 nm-thick device isolation film 12 is formed on themajor surface of the p-silicon substrate 10 by, e.g., the usual LOCOS todefine a device region 14. Then, about 10 nm-thick gate oxide films 16are formed in the device region 14 by thermal oxidation.

Subsequently, an about 150 nm-thick polycrystalline silicon filmcontaining a high concentration of P and an about 200 nm-thick siliconnitride film are successively formed by CVD, and then that portion ofthe silicon nitride film in the peripheral region is partially removedby the usual lithography and etching. This region is to be a gatecontact 82 through which wiring of the gate electrodes 22 are to be ledout.

Next, the silicon nitride film and the polycrystalline silicon film arepatterned together by the usual lithography and etching to form the gateelectrodes 20 of the memory cell transistors and the gate electrodes 22of a peripheral circuit.

Then, with the silicon nitride films 18 and the gate electrodes 20, 22as a mask, the source diffused layers 24 and the drain diffused layers26 of the memory cell transistors, and low-concentration diffused layers28 of the peripheral circuit transistors are formed by implanting, forexample, P ions under the conditions of a 40 keV acceleration energy anda 2×10¹³ ions cm⁻² dose (FIG. 20A).

Next, an about 100 nm-thick silicon nitride film is formed by CVD andthen is subjected to anisotropic etching by the use of CHF₃/H₂ gas toform the sidewall nitride films 30 of the silicon nitride film byself-alignment on the sidewalls of the patterned silicon nitride films18 and gate electrodes 20, 22.

The source diffused layers and the drain diffused layers 34 of theperipheral circuit n-transistors are formed by the usual lithography byselectively implanting in the peripheral circuit n-transistor region,for example, As ions under the conditions of a 40 keV accelerationenergy and a 4×10¹⁵ ions cm⁻² dose (FIG. 20B).

Then, the silicon oxide film 84 is deposited in a layer about 1 μm thickby CVD, and the surface thereof is polished by about 0.7 μm by CMP forplanarization. Then, the silicon nitride film 88 and the silicon oxidefilm 88 are successively grown respectively by 20 nm and 1.8 μm by CVD.

Next, a photoresist 90 is patterned by the usual lithography, and thenthe silicon oxide film 88 is etched by an etching gas, such as C₂F₆ orothers. Here, the silicon nitride film 86 is deposited on the planarizedsilicon oxide film 84, whereby a selectivity ratio with respect to thesilicon oxide film 88 can be about 100 and is sufficiently usable as theetching stopper for etching the silicon oxide film 88 (FIG. 20C).

Then, with the photoresist 90 as a mask, the silicon nitride film 86 andnext the silicon oxide film 84 are etched respectively by etching gasesof CHF₃/CF₄/Ar and C₂F₆.

Then, the photoresist 90 is removed, and the inter-layer insulation film36 with the through-holes 38 opened on the drain diffused layers 26 ofthe memory cell transistors, the through-holes 40 opened on the sourcediffused layers 24 of the memory cell transistors and the through-holes60 of the peripheral circuit region formed in (FIG. 21A).

Next, the capacitors, the bit lines, the wiring layers, etc. are formedby the fabrication steps exemplified in FIG. 17A showing the thirdembodiment and a DRAM of FIG. 21B comprising 1-transistor and1-capacitor memory cells is constituted.

As described above, according to the present embodiment, the etching ofthe very deep openings is divided in two steps, whereby the etching ofone step is relatively easy. Especially in the step of etching thesilicon oxide film 84 for diffusing the source diffused layers 24 andthe drain diffused layers 26, 34, the silicon oxide film 84 can be muchthinned, so that decreases of the thickness of the insulation films 42on the gate electrodes 20, 22, and decreases of the thickness of thedevice isolation film 12 occurring when the device isolation film 12 isexposed in the openings due to unalignment or other causes in thelithography step can be reduced.

Fifth embodiment

The semiconductor storage device according to a fifth embodiment of thepresent invention and a method for fabricating the same will beexplained with reference to FIGS. 22 to 24. Common members of thepresent embodiment with the semiconductor storage device and the methodfor fabricating the same according to the third embodiment shown inFIGS. 15 to 18 are represented by common reference numerals to simplifyand not repeat their explanation.

FIG. 22 is a diagrammatic sectional view of the semiconductor storagedevice according to the present embodiment, and FIGS. 23 and 24 aresectional views of the semiconductor storage device according to thepresent embodiment in the steps of the method for fabricating the same,which explain the method.

In the third embodiment, after the through-holes 38, 40, 60 are openedin the inter-layer insulation film 36, a Ti film and a TiN film aredeposited by CVD or collimated sputtering to form the capacitor storageelectrodes, 54, etc.

The deposited Ti film is essential to enable ohmic contact because theTi film is caused to react with the base silicon substrate 10 by thefollowing thermal treatment to form the titanium silicide film. The Tifilm must be deposited accurately on the bottoms of the through-holes38, 40, 60.

In a case that the through-holes are micronized and deeper with higherdevice integration, it is difficult to thus bury the Ti film.

In the present embodiment the semiconductor storage device and themethod for fabricating the same which can solve this problem will beexplained.

The semiconductor storage device according to the present embodiment ischaracterized in that buried conductors 92 are formed on the bottoms ofthrough-holes 38, 40, 60.

That is, an inter-layer insulation film 36 comprising a silicon oxidefilms 84, a silicon nitride films 86 and a silicon oxide films 88sequentially laid one on another is formed on a semiconductor substrate10 with memory cell transistors comprising gate electrodes 20, diffusedlayers 24, drain diffused layers 26 formed on.

In the inter-layer insulation film 36 there are formed the through-holes38 opened on the drain diffused layers 26, and through-holes 40 openedon the source diffused layers 24.

The buried conductors 92 of Ti and TiN films are formed on the bottomsof the through-holes 38, 40.

Capacitor storage electrodes 46 of the TiN film are formed on the insidewalls of the through-holes 40 and on the buried conductors 92 and areconnected to the source diffused layers 24 through the buried conductors92. Capacitor dielectric films 48 are formed on the inside surfaces andthe top surfaces of the capacitor storage electrodes 46. Capacitoropposed electrodes 54 are formed in the through-holes 40 with thecapacitor storage electrodes 46 and the capacitor dielectric filmsformed in, and on the inter-layer insulation film 36. Thus, capacitorscomprising the capacitor storage electrodes 46, the capacitor dielectricfilms 48 and the capacitor opposed electrodes 54 are constituted.

Contact conductor films 44 of the TiN film are formed on the insidewalls of the through-holes 38 and the buried conductors 92 and areconnected to the drain diffused layers 26 and bit lines 62 through theburied conductors 92.

Above the bit lines 62 there are formed wiring layers 70 through aninter-layer insulation film 64, and a DRAM comprising 1-transistor and1-capacitor memory cells is constituted.

Then, the method for fabricating the semiconductor storage deviceaccording to the present embodiment will be explained.

First an about 300 nm-thick device isolation film 12 is formed on themajor surface of a p-silicon substrate by, e.g., the usual LOCOS todefine a device region 14. Then, an about 10 nm-thick gate oxide film 16is formed in the device region 14 by thermal oxidation.

Subsequently, an about 150 nm-thick polycrystalline silicon filmcontaining a high concentration of P and an about 200 nm-thick siliconnitride film are successively formed by CVD, and then the siliconnitride film in the peripheral circuit region is partially removed bythe usual lithography and etching. This region is to be a gate contact82 through which wiring of the gate electrodes 22 are to be led out.

Then, the silicon nitride film and the polycrystalline silicon film arepatterned together by the usual lithography and etching to form the gateelectrodes of the memory cell transistors and the gate electrodes 22 ofthe peripheral circuits.

Then, with the silicon nitride films 18 and the gate electrodes 20, 22as a mask, the source diffused layers 24 and the drain diffused layers26 of the memory cell transistors, and low concentration diffused layers28 of transistors for peripheral circuits are formed (FIG. 23A).

Next, an about 100 nm-thick silicon nitride film is formed by CVD and issubjected to anisotropic etching using CHF₃/H₂ gas, and sidewall nitridefilms 30 of the silicon nitride film ar formed by self-alignment on thesidewalls of the patterned silicon nitride films 18 and gate electrodes20, 22.

Subsequently, in the n-transistor region for peripheral circuits, sourcediffused layers and drain diffused layers 34 of the peripheral circuitn-transistors are formed by, using the usual lithography, implanting,for example, As ions under the conditions of a 40 keV accelerationenergy and a 4×10¹⁵ ions cm⁻² dose (FIG. 23B).

Then, an about 1 μm thick silicon oxide film 84 is deposited by CVD, andthe surface thereof is polished by about 0.7 μm by CMP forplanarization. Then, a silicon nitride film 86 is grown in a 100nm-thickness by CVD.

Next, a photo-resist (not shown) is patterned by the usual lithography,and next the silicon nitride film 86 is etched with CHF₃/CF₄/Ar as anetching gas. Then, the silicon oxide film 84 is etched with C₂F₆ as anetching gas. Thus, the source diffused layers 24 and the drain diffusedlayers 26, 34 are exposed.

Then, a Ti film and a TiN film are successively grown respectively bycollimated sputtering in a 10 nm-thickness and CVD in a 200 nm-thicknessto be buried on the source diffused layers 24 and the drain diffusedlayers 26, 34. Then, the Ti film and the TiN film on the silicon nitridefilms 86 are removed by CMP to form the buried conductors 92 (FIG. 23C).

Next, an about 2 μm-thick silicon oxide film 88 is grown by CVD, and aphoto-resist is patterned by the usual lithography. Then, the siliconoxide film 88 is etched with an etching gas, such as C₂F₆ or others. Byusing C₂F₆ gas as an etching gas at this time, the etching can beautomatically stopped by the buried conductors 92 or the silicon nitridefilms 86.

Subsequently, the photo-resist is removed, and in the inter-layerinsulation film 36 are formed the through-holes 38 opened on the buriedconductors 92 on the drain diffused layer 26 of the memory celltransistors, the through-holes 40 opened on the buried conductors 92 onthe source diffused layers 24 of the memory cell transistors, and thethrough-holes 60 in the peripheral circuit region with the buriedconductors 92 formed on the bottoms (FIG. 24A).

Then, capacitors, bit lines, wiring layers, etc. are formed in the samesteps of FIG. 17A and its followers, and a DRAM comprising 1-transistorand 1-capacitor memory cells is constituted (FIG. 24B).

As described above, according to the present embodiment, in forming thethrough-holes, etc. of high aspect ratios, ohmic contacts are formed byforming in advance the buried conductors in regions where the buriedconductors contact the silicon substrate, whereby even in a case thatthe through-holes are micronized and deeper for higher deviceintegration, contact characteristics can be ensured on the bottoms ofthe through-holes.

In the present embodiment, one lithography step is added to form theburied conductors 92, but the use of SALICIDE (SALICIDE: Self-ALIgnedsiliCIDE; disclosed by, e.g., J. R. Pfiester, Technical Digest IEDM1990; p.241 (1990)) permits the conductors for contact to be formed onthe bottoms of the through-holes without adding one lithography step.

That is, after the insulation films 42 covering the gate electrodes 20,22 are formed, a Ti film for example, is deposited by sputtering on theentire surface of a semiconductor substrate 10 and then is subjected toa heat treatment. Then, silicidation takes place only on regions wherethe semiconductor substrate 10 and the deposited Ti film directlycontact each other, e.g., on the source diffused layers 24 and the draindiffused layers 26, 34.

Then, that portion of the Ti film unreacted is removed by, e.g., aquaregia, and a titanium silicide film can be formed by self-alignment onthe source diffused layers 24 and the drain diffused layers 26, 34.

After the titanium silicide films are thus formed on the source/draindiffused regions, the, semiconductor storage device is fabricated by themethod described in any one of the first to the fourth embodiments,whereby even in a case where the through-holes, etc. have high aspectratios, contact characteristics can be secured on the bottoms of thethrough-holes.

Other metal films which are applicable to silicide process are, e.g., Ta(tantalum), W (tungsten), Mo (molybdenum), etc.

Sixth Embodiment

The semiconductor storage device according to a sixth embodiment of thepresent invention and a method for fabricating the same will beexplained with reference to FIGS. 25 to 28B. Common members of thepresent embodiment with the semiconductor storage device and the methodfor fabricating the same according to the first embodiment shown inFIGS. 1 to 6 are represented by common reference numerals to simplifyand not repeat their explanation.

FIG. 25 is a diagrammatic sectional view of the semiconductor storagedevice according to the present embodiment, and FIGS. 26A-26B, 27A-27B,and 28A-28B are sectional views of the semiconductor storage deviceaccording to the present embodiment in the steps of the method forfabricating the same, which explain the method.

In the method for fabricating the semiconductor storage device accordingto the first embodiment, as shown in FIG. 4A, in forming the contactconducting films 44 and the capacitor storage electrodes 46, apolycrystalline silicon film containing a high concentration of P isformed, and then the polycrystalline silicon film on the inter-layerinsulation film 36 is removed by CMP.

In the simple polishing, however, pulverized objects generated uponpolishing intrude into the through-holes 38, 40 with a risk of loweredyields.

In the semiconductor storage device according to the first embodiment,because the contact conducting films 44 and the capacitor storageelectrodes 46 are formed of one and the same film, when the contactconducting films 44 are made thicker, an inside surface of thethrough-holes 40 of the capacitor storage electrodes 46 adversely have asmaller surface area. Consequently, to lower resistance the value of thecontact conducting films 44, a capacitance is sacrificed.

The resistance of the contact conducting films 44 is insignificant forabout 256M DRAMs, because a depth of the through-holes 40 can be set tobe below 2 μm, but resistance increases of the contact conducting films44 accompanying deeper through-holes 40 and thicker contact conductingfilms 44 for high integrations is a serious problem.

In the semiconductor storage device according to the present embodimentand the method for fabricating the same, in polishing step for formingthe contact conducting films 44 and the capacitor storage electrodes 46,pulverized objects are prevented from residing in the through-holes 38,40, and the contact conducting films 44 without sacrificingcapacitances.

The semiconductor storage device according to the present embodiment ischaracterized in that columnar conductors 112, 114 are formedrespectively in the through-holes 38, 40.

That is, the columnar conductor 112 connected to the contact conductingfilm 44 at the bottom and having capacitor dielectric films 48 formed onthe sidewalls are formed in the through-holes 38, and the columnarconductors 114 connected to the capacitor storage electrodes 46 at thebottoms and having the capacitor dielectric films 48 formed on thesidewalls are formed in the through-holes 40.

By thus providing the columnar conductors, electric passageinterconnecting drain diffused layers 26 and a bit lien 62 areconstituted in the through-holes 38 by the contact conducting films 44and the columnar conductors 112. An electric resistance at the bit linecontacts can be drastically decreased.

By forming the columnar conductors 114 in the through-holes 40, thecapacitor dielectric films 48 are formed on the sidewalls thereof. Thecapacitor area is larger, and a larger capacitance can be obtained.

Then, the semiconductor storage device according to the presentembodiment will be explained.

First, by the same method for fabricating the semiconductor storagedevice according to the first embodiment shown in FIGS. 3A to 3D, aninter-layer insulation film 36 with the through-holes 38 formed in onthe drain diffused layers 26 and the through-holes 40 formed in on thesource diffused layers 24 is formed (FIG. 26A). A size of thethrough-holes 38 is, e.g., 0.3×0.3 μm, and that of the through-holes 40is, e.g., 0.3×0.6 μm.

Next, a polycrystalline silicon film 106 containing a high concentrationof P is formed in an about 30 nm-thickness by CVD.

Subsequently, a silicon oxide film is grown in an about 80 nm-thicknessby CVD using, e.g., TEOS (tetraethoxysilane) as a main material, andthen the entire surface of the silicon oxide film is etched verticallyby RIE to form the sidewalls 108 (FIG. 26B).

As a result, [300−2×(30+80)]×[300−2×(30+80] nm, i.e., 80×80 gaps areleft in the through-holes 38, and [300−2×(30+80)×[600−2×(30+80)] nm,i.e., 80×380 nm gaps are left.

Then, an about 200 nm-thick polycrystalline silicon film 110 isdeposited by CVD (FIG. 27A). It is preferred to set a thickness of apolycrystalline silicon film 110 to be deposited so that the gaps in thethrough-hoes 38, 40 are completely buried, and the entire surface isgenerally substantially flat.

Then, the entire surface is polished by CMP. In this polishing somewhatover-polishing is conducted so that the top surfaces of the sidewalls108 are completely exposed. Thus, the surface is planarized with thecontact conducting films 44 of the polycrystalline silicon film 106, thecolumnar conductors 112 of the polycrystalline silicon film 110 and thesidewalls 108 completely buried in the through-holes 38 and with thecapacitor storage electrodes 46 of the polycrystalline silicon film 106,the columnar conductors 114 of the polycrystalline silicon film 110 andthe sidewalls 108 completely buried in the through-holes 40 (FIG. 27B).

Subsequently, the substrate is immersed in a solution of, e.g.,HF:NH₄F=1:5, whereby the sidewalls 108 are selectively removed. Thus,voids 116 are formed in the through-holes 38, 40 (FIG. 28A).

Then, the capacitor dielectric films 48, the capacitor opposedelectrodes 54 and bit lines 62, wiring layers 70, etc. are formed by thesame steps of the method for fabricating the semiconductor storagedevice according to, e.g., the first embodiment shown in FIG. 4B to FIG.6B (FIG. 28B).

As described above, according to the present embodiment, the columnarconductors 114 are formed in the through-holes 40, whereby the columnarconductors 114 function as capacitor storage electrodes in addition tothe capacitor storage electrodes 46, whereby a surface area of thecapacitors can be increased by a surface area of the columnar conductors114. Accordingly, even in a case that the same capacity as thesemiconductor storage device of FIG. 1 is necessary, the through-holes40 can be made shallow.

Lead out electrodes at the bit line contacts are constituted by thecontact conducting films 44 and the columnar conductors 112, whereby theresistance of the lead out electrodes can be lowered. As describedabove, a capacitance can be increased, which makes it possible toshallow the through-holes 38. This makes it possible to make theresistance of the lead out electrodes low.

In the semiconductor storage device according to the present embodiment,a peripheral circuit contact holes 60 have the same structure as in thesemiconductor storage device according to the variation of the firstembodiment but may have a different structure. For example, as in thesemiconductor storage device of FIG. 2 according to the firstembodiment, via holes 66 are opened on the wiring layers 68 to form thewiring layers 70.

Seventh Embodiment

The semiconductor storage device according to a seventh embodiment ofthe present invention and a method for fabricating the same will beexplained with reference to FIGS. 29 to 31B. Common members of thepresent embodiment with the semiconductor storage device and the methodfor fabricating the same according to the first embodiment shown inFIGS. 1 to 7 are represented by common reference numerals to simplifyand not repeat their explanation.

FIG. 29 is a diagrammatic sectional view of the semiconductor storagedevice according to the present embodiment, and FIGS. 30A-30B, and31A-31B are sectional views of the semiconductor storage deviceaccording to the present embodiment in the steps of the method forfabricating the same, which explain the method.

In the semiconductor storage device according to one variation of thefirst embodiment, which is shown in FIG. 7, the through-holes 60 ofperipheral circuits are opened after the inter-layer insulation film 64have been formed to contact the wiring layers 70 directly to thecapacitor opposed electrodes 54, and the source/drain diffused layers 34of the peripheral circuit transistors, whereby lithography steps aredecreased.

The wiring layers 70 must contact concurrently to the source/draindiffused layers 34 of peripheral circuit transistors, the capacitoropposed electrodes 54, the bit lines 62, etc., and, to this end, thethrough-holes 60, the contact holes 59, etc. have various depths fromvery deep to shallow.

In etching holes of such various depths, it takes a long period of timefor the source/drain diffused layers 34 of the peripheral circuittransistors to be exposed after the surfaces of the bit lines 62 and thecapacitor opposed electrodes 54 are exposed, and the surfaces of the bitlines 62 and the capacitor opposed electrodes are continuously exposedto an etching gas for the long period of time. Especially in a case thatthe bit lines 62 are formed of a columnar crystal metal thin film, suchas tungsten or others, sometimes the ground insulation film is etchedthrough gaps between crystals, causing damages. As a result, the bitlines 62 and the silicon substrate 10 may be short-circuited.

In the semiconductor storage device according to the present embodimentand the method for fabricating the same, the through-holes of variousdepths can be simultaneously formed.

The semiconductor storage device according to the present embodiment ischaracterized in that an inter-layer insulation film 53 having etchingcharacteristics different from those of inter-layer insulation film 64,36 is formed on capacitor opposed electrodes 54, and etching stoppers118 which are laminated films of conducting films 124, and insulationfilms 126 having etching characteristics different from those of theinter-layer insulation film 64, 36 are disposed below parts of bit lines62 in regions for contact holes 120 connecting the bit lines 62 andwiring layers 70 above the bit lines 62.

That is, the wiring layers 70 formed on the inter-layer insulation film64 are connected to gate electrodes 22 of peripheral circuit transistorsthrough through-holes 122, connected to source/drain diffused layers 34of the peripheral circuit transistors through through-holes 60,connected to the capacitor opposed electrodes 54 through contact holes59, and connected to the bit lines 62 through contact-hole 120.Inter-layer insulation film 53 of silicon nitride film is formed on thecapacitor opposed electrodes 54. Below the laminated films 118 of theconducting films 124 and silicon nitride films 126 are provided belowthe contact holes 120 opened on the bit lines 62.

Then, the method for fabricating the semiconductor storage deviceaccording to the present embodiment will be explained with reference toFIGS. 30A to 31B.

The capacitor opposed electrodes 54 are formed by the same steps of themethod for fabricating the semiconductor storage device according to thefirst embodiment shown in FIGS. 3A to 5A. At this time, the laminatedfilms 118 of the conducting layers formed of the same film as thecapacitor opposed electrodes 54, and the insulation films 126 formed ofthe inter-layer insulation film 53 have been provided in regions forcontacts to be formed between the bit lines 62 and the wiring layers 70above the bit lines 62 (FIG. 30A). The inter-layer insulation film 53 isformed of a material, e.g., silicon nitride film, having etchingcharacteristics different from those of the inter-layer insulation film36 and the inter-layer insulation film 64 to be deposited on theinter-layer insulation film 36.

Then, the inter-layer insulation film 64 is deposited on the entiresurface to planarize the surface. Then, a photo-resist 72 with a patternof the through-holes and the contact holes formed on is formed by theusual lithography. Subsequently, with the photo-resist 72 as a mask, theinter-layer insulation film 64 and the inter-layer insulation film 36are etched. The inter-layer insulation film 64, 36 are etched underconditions which allow a sufficient selection ratio with respect to theinter-layer insulation film 53.

In this etching, because the through-holes 59 formed on the capacitoropposed electrodes 54 and the contact holes 120 formed on the bit lines62 are shallower than the through-holes 60 opened on the source/draindiffused layers 34 of the peripheral circuit transistors and thethrough-holes 122 opened on the gate electrodes 22 of the peripheralcircuit transistors, that portion of the inter-layer insulation film 64on the bit lines 62 is completely removed to expose the surface of thebit lines 62 to an etching gas before the through-holes 60, 122 arecompletely opened. The inter-layer insulation film 53 is exposed on thecapacitor opposed electrodes 54 but is not substantially etched becausethe inter-layer insulation film 53 is formed of silicon nitride filmwhose etching characteristics are different from those of theinter-layer insulation film 64 of silicon oxide film (FIG. 30B).

The etching is further set on to expose the source/drain diffused layer34 of the peripheral circuit transistors (FIG. 31A). At this time, inthe case that the bit lines 62 are formed of a columnar crystalmaterial, e.g., tungsten, the etching sometimes reaches even the lowerlayer film at the crystal boundaries. This is emphatically shown in FIG.31A by extinguishing the bit lines 62 themselves. Because of theinsulation films 126 of silicon nitride film formed below the bit lines62, the inter-layer insulation film 36 is not damaged.

Then, the silicon nitride film is removed by etching using, e.g.,CF₄/CHF₃/He gas, whereby the inter-layer insulation film 53 on thecapacitor opposed electrodes 54 and the insulation films 42 on the gateelectrodes of the peripheral circuit transistors are removed, and thethrough-holes 60, 122 and the contact holes 59, 120 are completelyopened (FIG. 31B). At this time, the insulation films 126 below the bitlines 62 are also removed, but the etching is stopped by the conductingfilms 124 below the insulation films 126.

An etching gas used in this etching can have a short etching timebecause the etching speed of silicon is low, and the residual siliconnitride films are not thick. Accordingly, etching of the already exposedsource/drain diffused layers 34 of the peripheral circuit transistors isignorable.

Thus, all the through-holes and the contact holes can be formed withoutany inconvenience.

As described above, according to the present embodiment, the laminatedfilm 118 is formed in advance in the regions for the contacts betweenthe bit lines 62 and the wiring layers 70 above the bit lines 62,whereby the inter-layers insulation film 36 below the bit lines 62 isnot etched in forming the through-holes 60, 120 of the peripheralcircuit region, and short-circuit between the bit lines 62 and thesemiconductor substrate 10, etc. can be prevented.

Eighth Embodiment

The semiconductor storage device according to an eighth embodiment ofthe present invention will be. explained with reference to FIGS. 32A to38. Common members of the semiconductor storage device according to thepresent embodiment and the method for fabricating the same with thesemiconductor storage device according to the first embodiment and themethod for fabricating the same are represented by common referencenumerals to simplify and not to repeat their explanation.

FIGS. 32A-32D are views for explaining the problems of the method forfabricating the semiconductor storage device according to the firstembodiment. FIG. 33 is a plan view of the semiconductor storage deviceaccording to the present embodiment, which explain the structurethereof. FIG. 34 is a diagrammatic sectional view taken along the line34—34 of FIG. 33, of the semiconductor storage device according to thepresent embodiment, which explains the structure thereof. FIGS. 35A-35B,36A-36B, 37A-37B, and 38 are sectional views of the semiconductorstorage device according to the present embodiment in the steps of themethod for fabricating the same, which explain the method forfabricating the same.

In the method for fabricating the semiconductor storage device accordingto the first embodiment, which is shown in FIGS. 3A to 6, the contactconducting films 44 and the capacitor storage electrodes 46 are formedby self-alignment with the gate electrodes 20 of the memory celltransistors. According to this method, it is not necessary to consider apositioning allowance between the gate electrodes 20 and thethrough-holes 38. This results in a merit that the memory cells can havesmaller areas.

Micronization of the memory cells, however, abruptly increases depths ofthe through-holes 38, which abruptly makes the etching of thethrough-hoes difficult. Problems of the semiconductor storage deviceaccording to the first embodiment will be explained.

In the steps of the method for fabricating the semiconductor storagedevice, which are shown in FIGS. 3A and B, if dust 130 stays on thepolycrystalline silicon film 128 when the silicon nitride film 18 isdeposited on the polycrystalline silicon film 128 to be the gateelectrodes 20, the silicon nitride film 18 grown on the polycrystallinesilicon film 128 in a region with the dust 130 staying on bulges (FIG.32A).

When the silicon nitride film 18 is etched with the photo-resist 72patterned in the gate electrodes 20, the polycrystalline silicon filmbulges around the dust 130, and a part of the polycrystalline siliconfilm remains as residue 132 (FIG. 32B).

When the base polycrystalline silicon film 128 is etched in this state,the residue 132 functions as a mask, adversely leaving a part of thepolycrystalline silicon film 128 as residue 134 (FIG. 32C).

Then, when the through-holes 38, 40 are formed by the same way as by themethod for fabricating the semiconductor storage device shown in FIGS.3B to 3D, the residue 134 is adversely exposed in the through-holes 38,with a result of short-circuit with the contact conducting films 44.

Thus, the structure of the semiconductor storage device according to thefirst embodiment is very sensitive to dust, and there is a risk thatthis may result in decrease of yields. If simply yields are decreased,it can be solved by means of redundancy or other means. Shirt circuitbetween the bit lines 62 and the word lines 20 is a serious problem.That is, a current regularly flows from the bit lines 62 to the wordlines 20 when in a standby operation because a potential of the bitlines 62 is set to half the source voltage, and a potential of the wordlines 20 is set at zero. The current consumption is therefore increasedwhen in a standby operation, which cannot be remedied by the usualredundancy.

The semiconductor storage device according to the present embodiment andthe method for fabricating the same can solve the problem the firstembodiment cannot solve.

As shown in the plan view of FIG. 33 and the sectional view of FIG. 34,the semiconductor storage device according to the present embodiment ischaracterized in that fine through-holes 38 for connecting bit lines 62and drain diffused layers 26, and find through-holes 40 for contact ofcapacitor storage electrodes 46 are formed, and the capacitor storageelectrodes 36 are formed in larger openings 142 formed on thethrough-holes 40.

This structure can sufficiently space the contact conducting films 44buried in the through-holes 38 from the gate electrodes 20, wherebyshort-circuit between the gate electrodes 20 and the bit lines 62 can bedrastically decreased.

A polycrystalline silicon film 140 is present in columnar projections inthe openings 142, whereby larger capacitances can be obtained.

Next, the method for fabricating the semiconductor storage deviceaccording to the present embodiment will be explained.

First, an about 300 nm-thick device isolation film 12 is formed on themajor surface of a silicon substrate. 10 to define a device region 14by, e.g., the usual LOCOS. Then, an about 10 nm-thick gate oxide film 16is formed in the device region by thermal oxidation.

Subsequently, an about 150 nm thick polycrystalline silicon filmcontaining a high concentration of P is formed by CVD and is patternedby the usual lithography and etching to form the gate electrodes 20.

In the present embodiment the polycrystalline silicon film alone ispatterned to form the gate electrodes 20, but as in the firstembodiment, a polycrystalline silicon film and a silicon nitride filmare successively formed, and the laminated film of these films may bepatterned together. In the latter case, accidental exposure of the gateelectrodes 20 in the through-holes 38, 40 can be prevented in formingthe through-holes 38, 40.

Then, source diffused layers 24 and drain diffused layers 26 of thememory transistors are formed by, with the gate electrodes 20 as a mask,implanting, e.g., P ions under the conditions of an acceleration energyof 20 keV and a dose of 2×10¹³ ions cm⁻². Although not shown in thepresent embodiment, the thus-formed diffused layers become n⁻ layers ofthe LDD structure of peripheral circuit n-transistors (FIG. 35A).

Then, an about 100 nm-thick silicon nitride film is formed by CVD andthen is subjected to anisotropic etching to form by self-alignmentsidewall nitride films 30 on the sidewalls of the gate electrodes 20(FIG. 35B). The sidewalls may be formed of silicon oxide film.

Subsequently, source/drain diffused layers of peripheral circuitn-transistors are formed by selectively implanting, for example, As ionsunder the conditions of a 40 keV acceleration energy and a 4×10¹⁵ ionscm⁻² dose. Thus, peripheral circuit transistors of the LDD structure canbe formed.

Then, an about 2 μm thick BPSG film is deposited by CVD to form aninter-layer insulation film 36.

Then, an about 100 nm-thick polycrystalline silicon film is formed onthe inter-layer insulation film 36 by CVD. Next, the polycrystallinesilicon film is patterned by the usual lithography and etching to form apolycrystalline silicon pattern 136.

Subsequently, an about 150 nm-thick polycrystalline silicon film isdeposited and then etched by RIE to form polycrystalline siliconsidewalls 138 on the sidewalls of the patterned polycrystalline siliconpatterns 136 (FIG. 35C).

Then, with the thus-formed polycrystalline silicon pattern 136 and thepolycrystalline silicon sidewalls 138 as a mask, the inter-layerinsulation film 36 is etched to form the through-holes 40 opened on thesource diffused layers 24 and the through-holes 38 opened on the draindiffused layers 26 (FIG. 36A).

The thus-formed through-holes 38, 40 are opened with the polycrystallinesilicon patterns 136 and the polycrystalline silicon sidewalls 138 as amask, and these through-holes can have fine openings of, e.g., 0.1 μm,which is below minimum resolution dimensions of an exposure device.

The method in which the through-holes 38, 40 are formed needs aconsiderable number of fabrication steps. The through-holes 38, 40 canbe formed by electron beam lithography by limiting regions in which thethrough-holes 38, 40 are formed, e.g., to the memory cells. Generally,electron beam lithography adds time to the throughput, but theadditional time can be compensated by the fabrication step numberdifference of the above-described method, whereby it is possible toshorten the throughput time.

Then, an about 100 nm thick polycrystalline silicon film 140 isdeposited by CVD to fill the through-holes 38, 40 (FIG. 36B). This stepis not essential but is effective to increase a capacitance and protectthe base substrate from damages by the etching. This will be describedlater.

Subsequently, the polycrystalline silicon film 140, the polycrystallinesilicon patterns 136, the polycrystalline silicon sidewalls 138 and theinter-layer insulation film 36 are patterned by the usual lithographyand etching to form openings 142 in regions for capacitors to be formedin (FIG. 37A). At this time, the polycrystalline silicon film 140 whichhas been buried in the through-holes 40 is left in columnar projectionswhich keep the surface of the silicon substrate 10 from direct damage bythe etching.

It is necessary to pause the etching of the inter-layer insulation film36 therein. In a case that the etching cannot have sufficient precision,it is possible that the inter-layer insulation film 36 is a laminatedfilm of, e.g., a silicon nitride film and a BPSG film, and the etchingof the openings 142 are stopped on the silicon nitride film. This addsto a number of the fabrication steps but facilitates the depth controlof the openings 142, lowers capacitance disuniformity, and stabilizescharacteristics.

Then, an about 20 nm-thick polycrystalline silicon film is deposited byCVD and is polished by CMP until the inter-layer insulation film 36 isexposed on the surface. Thus, capacitor storage electrodes 46 are formedin the openings 142, and contact conducting films 44 are formed in thethrough-holes 38 (FIG. 37B).

The polycrystalline silicon films 140 left in the columnar projectionswithin the openings 142 add to a surface area of the capacitor storageelectrodes 46. This increases a capacitance.

After the contact conducting films 44 and the capacitor storageelectrodes 46 are thus formed, the capacitor opposed films 48, thecapacitor opposed electrodes 54, the bit lines 62, the wiring layers 70,etc. are formed in the same way as in the method for fabricating thesemiconductor storage device according to the first embodiment (FIG. 38)

Thus, according to the present embodiment, the through-holes opened onthe source diffused layers 24, and the through-holes 38 opened on thedrain diffused layers 26 can have very small bores, whereby even whenetching residues of the gate electrodes 20 take place, short-circuitbetween the bi line 62 and the gate electrodes 20 can be much reduced.

A surface area of the capacitor storage electrodes 54 is determined bythe openings 142 separately formed, and the above-described effect canbe produced without decrease a surface area of the capacitor storageelectrodes 46.

The columnar projections are left in the openings 142 by depositing thepolycrystalline silicon film 140 before the formation of the openings142, whereby a capacitance can be increased, and a depth of thethrough-holes can be decreased for a certain capacitance.

In the present embodiment, the conducting film buried in thethrough-holes 38, 40 is polycrystalline silicon film but may be variousconductor films as exemplified in the third embodiment.

Ninth Embodiment

The method for fabricating the semiconductor storage device according toa ninth embodiment will be explained with reference to FIGS. 39A to 40B.Common members of the ninth embodiment with the first embodiment ofFIGS. 1 to 7 and with the semiconductor storage device according to thethird embodiment and the method for fabricating the same are representedby common reference numerals to simplify and not repeat theirexplanation.

FIGS. 39A-39B, and 40A-40B are sectional views of the semiconductorstorage device in the steps of the method for fabricating the same,which explain the method.

In the method for fabricating the semiconductor storage device accordingto the first embodiment, as shown in FIG. 4A, in forming the contactconductor films 44 and the capacitor storage electrodes 46, apolycrystalline silicon film containing a high concentration of P isformed, and then the polycrystalline silicon film on the inter-layerinsulation film 36 is removed by CMP.

In the method for fabricating the semiconductor storage device accordingto the third embodiment, as shown in FIG. 17A, in forming the contactconductor films 44, the capacitor storage electrodes 46 and theconductor films 80, a Ti film and a TiN film are successively formed,and then the TiN film and the Ti film on the inter-layer insulation film36 are removed by CMP.

As described in the sixth embodiment, however, the contact conductorfilms 44 and the capacitor storage electrodes 46 are formed in thethrough-holes 38, 40, 60, pulverized objects generated upon thepolishing intrude into he through-holes 38, 40, 60 with a risk oflowering yields.

When the pulverized objects intrude into the through-holes 40, thethrough-holes 40 are filled up, with results that a capacity cannot beensured, and also a breakdown voltage is lowered.

In the third embodiment, by the use of lithography in place of CMP, aphoto-resist is left in the through-holes 38, 40, 60, and then with thephoto-resist as a mask the Ti film and the TiN film are etched off. Thismethod cannot control the etching at the end point.

The control in terms of time needs overetching, because residues atplaces other than within the through-holes 38, 40, 60 causeshort-circuit between, e.g., the bit lines 62 and the capacitor storageelectrodes 46. The overetching etches even the capacitor storageelectrodes 46 on the sidewalls of the through-holes 40, with a result ofa decreased capacitance.

In the method for fabricating the semiconductor storage device accordingto the present embodiment, the contact conductor films 44 and thecapacitor storage electrodes 46 and the conductor films 80 can be formedby CMP without intrusion of the pulverized objects, etc. into thethrough-holes 38, 40, 60.

The present embodiment to be described below is applied to the methodfor fabricating the semiconductor storage device according to the thirdembodiment but may be applicable to the method for fabricating thesemiconductor storage device according to the other embodiments.

Through-holes 38, 40, 60 are formed in an inter-layer insulation film 36in the same way as in the method for fabricating the semiconductorstorage device according to the third embodiment shown in FIGS. 16A to16C.

Then, an about 10 nm-thick Ti film and an about 30 nm-thick TiN film aresuccessively formed by CVD to form a conductor film 144 (FIG. 39A).

Subsequently, a pigment-containing resist is applied to the surface toform an about 3 μm-thickness photo-resist 72, whereby the through-holes38, 40, 60 are completely filled with the photo-resist (FIG. 39B).Photosensitive polyimide may be used in place of the photo-resist 72.

Next, the entire surface of the photo-resist 72 is exposed to leave thephoto-resist 72 only in the through-holes 38, 40, 60 (FIG. 40A).

Then, the conductor film 144 on the inter-layer insulation film 36 isremoved by CMP. At this time, pulverized objects, etc. generated by thepolishing do not intrude into the through-holes 38, 40, 60 because ofthe photo-resist 72 buried in the through-holes 38, 40, 60. Thus,contact conductor films 44, capacitor storage electrodes 46 andconductor films 80 are formed.

In place of exposing the entire surface of the photo-resist 72, thephoto-resist 72, the TiN film and the Ti film may be removed by CMP.

The photo-resist 72 left in the through-holes 38, 40, 60 are removed byan aqueous solution of hydrogen peroxide (FIG. 40B).

Subsequently, the semiconductor storage device is fabricated by themethod shown in FIGS. 17A to 18B.

Thus, in the present embodiment, in the polishing step for forming thecontact conductor films 44, the capacitor storage electrodes 46 and theconductor films 80, the photo-resist 70 is buried in the through-holes38, 40, 60, whereby none of pulverized objects generated by thepolishing and a polishing agent intrude into the through-holes 38, 40,60, whereby decrease of yields caused thereby can be prevented.

In the present embodiment, the bit line contacts and the contacts of theperipheral circuit region have the same structure as in thesemiconductor storage device according to the third embodiment, but thecontacts of the peripheral circuit region may have the structure of thesemiconductor storage devices according to the first and the secondembodiments.

The structure of the semiconductor storage device according to thepresent embodiment is applicable to other embodiments of the presentinvention.

Tenth Embodiment

The semiconductor storage device according to a tenth embodiment of thepresent invention and the method for fabricating the same will beexplained with reference to FIGS. 41 to 43B. Common members of thepresent embodiment with the semiconductor storage device according tothe ninth embodiment and the method for fabricating the same arerepresented by common reference numerals to simplify or not repeat theirexplanation.

FIG. 41 is a diagrammatic sectional view of the semiconductor storagedevice according to the present embodiment showing the structurethereof. FIGS. 42A-42B, and 43A-43B. are sectional views of thesemiconductor storage device in the steps of the method for fabricatingthe same explaining the method.

The method for fabricating the semiconductor storage device according tothe present embodiment can form, as can the ninth embodiment, thecontact conducting films, the capacitor storage electrodes, etc. by CMPwithout intrusion of pulverized objects, etc. into the through-holes.

The semiconductor storage device according to the present embodiment ischaracterized in that an insulation film having etching characteristicsdifferent from those of an inter-layer insulation film 36 is formed onthe top of the inter-layer insulation film 36.

Then, the method for fabricating the semiconductor storage deviceaccording to the present embodiment will be explained.

In the same way as the method for fabricating the semiconductor storagedevice according to the third embodiment shown in FIGS. 16A and 16B,memory cell transistors and peripheral circuit transistors are formed ona semiconductor substrate 10.

Next, an about 2 μm-thick silicon oxide film and an about 50 nm-thicksilicon nitride film are successively formed by CVD to form theinter-layer insulation film 36, and a silicon nitride film 146 is formedon the top of the inter-layer insulation film 36.

Subsequently, through-holes 38, 40, 60 are opened in the inter-layerinsulation film 36 of the two layer-structure of the silicon nitridefilm 146 and the silicon oxide film (FIG. 42A).

Then, conducting films 144 constituted by an about 10 nm-thick Ti filmand an about 30 nm-thick TiN film, and an about 0.15 μm-thick siliconoxide film 148 are deposited by CVD (FIG. 42B). The silicon oxide film148 completely fills the through-holes 38, 40, 60.

Then, the silicon oxide film 148 is removed onto the conducting films144 by CMP, and then the conducting films 144 are removed onto thesilicon nitride films 146 (FIG. 43A). Thus, contact conducting films 44,capacitor storage electrodes 46 and conducting films 80 are formed.

By thus forming the contact conducting films 44, the capacitor storageelectrodes 46 and the conducting films 80, pulverized objects generatedupon the polishing and the polishing agent are hindered from intrudinginto the through-holes 38, 40, 60.

Subsequently, the silicon oxide films 148 are removed by wet etchingusing, e.g., an aqueous solution of hydrogen fluoride (FIG. 43B).

Then, the semiconductor storage device is formed by the method forfabricating the same shown in FIGS. 17A to 18B.

Thus, according to the present embodiment, the silicon oxide film 148 isfilled in the through-holes 38, 40, 60, before the polishing for formingthe contact conductor films 44, the capacitor storage electrodes 46 andthe conductor films 80, whereby none of pulverized objects generatedupon the polishing and a polishing agent intrude into the through-holes38, 40, 60, with a result that yields drop due to their intrusion can beprevented.

Eleventh Embodiment

The semiconductor storage device according to the eleventh embodiment ofthe present invention and the method for fabricating the same will beexplained with reference to FIGS. 44 to 47.

FIG. 44 is a diagrammatic sectional view of the semiconductor storagedevice according to the present embodiment. FIGS. 45A-45B, 46A-46B, and47 are sectional views of the semiconductor storage device according tothe present embodiment in the steps of the method for fabricating thesame, which explain the method.

In the semiconductor storage device according to the present embodimentand the method for fabricating the same, the methods for fabricating thesemiconductor storage devices according to the fourth and the tenthembodiments are applied to a semiconductor storage device includingdouble-side cylinder capacitors.

That is, as shown in FIG. 44, capacitor storage electrodes 46 areconstituted by contacts 46 a formed on the inside walls and bottoms ofthrough-holes 40 formed in an inter-layer insulation film 36 formed of asilicon oxide film 84 and a silicon nitride film 86, and projections 46b formed continuously on the contacts 46 a. Capacitor dielectric films48 are formed covering the interior of the capacitor storage electrodes46 and the exteriors of the projections 46 b. Capacitor opposedelectrodes are formed covering at least a part of the capacitordielectric films 48. Thus, the double-sided cylinder capacitors areformed.

An inter-layer insulation film 36 having the through-holes 40 is formedof a laminated film of films having different etching characteristicsfrom each other. That is, in the semiconductor storage device accordingto the present embodiment, the inter-layer insulation film 36 comprisesilicon oxide films 84 and silicon nitride films 86.

Then, the method for fabricating the semiconductor storage deviceaccording to the present embodiment will be explained.

First, in the same way as in the method for fabricating thesemiconductor storage device according to the fourth embodiment shown inFIGS. 20A to 21A, an inter-layer insulation film of the three-layerstructure of the silicon oxide film 84, the silicon nitride film 86 andthe silicon oxide film 88 is formed, and the through-holes 40 are openedtherein. In the method for fabricating the semiconductor storage deviceaccording to the fourth embodiment, the through-holes 38 opened on thedrain diffused layers 26 are concurrently opened, but the through-holes38 are not formed concurrently in the present embodiment (FIG. 45A).

Then, a conducting layer 144 of an about 50 nm-thick polycrystallinesilicon film heavily doped with P, and an about 0.15 μm-thick siliconoxide film 148 are deposited by CVD (FIG. 45B). Thus, the through-holes40 are completely filled with the silicon oxide film 148.

Subsequently, the silicon oxide film 148 is removed by CMP onto theconducting film 144. Then, the conducting film 144 is removed onto thesilicon oxide film 88 (FIG. 46A). Thus, capacitor storage electrodes 46are formed.

By thus forming the capacitor storage electrodes 40, pulverized objectsgenerated upon polishing the conducting film 144 and a polishing agentare hindered from intruding into the through-holes 40.

Then, wet etching using, e.g., an aqueous solution of hydrogen fluoridefollows. The silicon oxide film 148 and the silicon oxide film 88 areremoved by this etching to expose the capacitor storage electrodes 46into cylindrical projections (FIG. 46B).

Then, the capacitor dielectric film 48 and the capacitor opposedelectrodes 54 are formed, and an inter-layer insulation film 64 isdeposited.

Subsequently, through-holes 38 are opened through the inter-layerinsulation film 64, the silicon nitride film 86 and the silicon oxidefilm 84, and bit lines 62 are formed filling the through-holes 38 (FIG.47).

The semiconductor storage device is thus fabricated, whereby DRAM cellshaving capacitors of a two-sided cylinder structure are fabricated.

As described above, according to the present embodiment, by burying thesilicon oxide film 148 in the through-holes 40 before the step of thepolishing for forming the capacitor storage electrodes 46, pulverizedobjects generated by the polishing and a polishing agent are hinderedfrom intruding into the through-holes 40, whereby in the semiconductorstorage device including cylinder capacitors, yield drops due to theirintrusion can be prevented.

In the present embodiment, the bit lines 62 formed on the inter-layerinsulation film 64 are directly connected to the drain diffused layers26, but as in the semiconductor storage device according to the firstembodiment, the bit lines 62 may be connected to the drain diffusedlayers 26 through the contact conducting films 44 formed concurrentlywith the formation of the capacitor storage electrodes 46.

Twelfth Embodiment

The structure of the semiconductor storage device according to thetwelfth embodiment of the present invention will be explained withreference to FIGS. 48A to 49. Common members of the present embodimentwith the semiconductor storage devices according to the first to thethird embodiments are represented by common reference numerals tosimplify or not to repeat their explanation.

FIG. 48A is a plan view of the semiconductor storage device according tothe present embodiment. FIGS. 48B and 48C are sectional views of thesemiconductor storage device according to the present embodiment, whichshow the structure thereof. FIG. 49 is a view which exemplifies thestructure of the peripheral circuit of the semiconductor storage deviceaccording to the present embodiment.

The above-described first to the third embodiments make the best use ofself-alignment process to dispense with various self-alignmentallowances. Accordingly, it is possible to arrange word lines and bitlines in a line/space (L/S) arrangement of minimum processing dimension.

If the word lines and the bit lines are processed in a L/S of minimumprocessing dimensions, no overlap allowance, etc. between contact holesand wiring layers can be secured, and lines cannot be bent. To realizesuch memory cells, in addition to the means described in theabove-described embodiments, it is necessary to lay out a pattern inconsideration of a peripheral circuit layout, etc.

The structure of the semiconductor storage device according to thepresent embodiment can realize the semiconductor storage devicesaccording to the first to the third embodiments, taking intoconsideration a layout of a peripheral circuit.

In the semiconductor storage device according to the present embodiment,as shown in FIG. 48A, the bit lines 62 and word lines 20 which have beenpatterned in minimum processing dimensions perpendicularly intersecteach other. A problem with such layout is overlap allowances, etc.between the bit line contact holes and the bit lines.

The bit lines 62 have to contact conducting films 44 as shown in thesectional view along the line 48B—48B in FIG. 48A, which is shown inFIG. 48B, and to this end the contact conducting films 44 have to beexposed in the bit line contact holes 58.

However, when pattern edges of the bit lines are adversely formed in thebit line contact holes 58 by unalignment in patterning the bit lines 62,the contact conducting films 44, etc. are etched in forming the bitlines 62, and steps are unfavorably increased. Accordingly, it isrequired that a width of the bit line contact holes 58 is smaller than awidth of the bit lines 62 as shown in FIG. 48C which is the sectionalview along the line 48C—48C in FIG. 48A.

On the other hand, it is required that the bit lines 62, which are to beconnected to polycrystalline silicon films 50 buried in thethrough-holes 38, are sufficiently spaced from the through-holes 38 informing capacitor opposed electrodes 54 so that the polycrystallinesilicon films 50 buried in the through-holes 38 are left connected tothe capacitor opposed electrodes 54. Thus, it is preferable that the bitline contact holes 58 are wide.

To satisfy these requirements of the bit line contact holes 58, whichare contradictory with each other, the thickness of the contactconducting films 44 and the width of the sidewall oxide films 56 must beoptimized.

In a case, for example, that the bit lines 62 are patterned in a 0.3 μmL/S, and the through-holes are opened by 0.3 μm, an overlap of the bitlines 62 is, e.g., 0.07 μm, and a gap between the polycrystallinesilicon films 50 and the capacitor opposed electrodes 54 is 0.1 μm inconsideration of unalignment of the bit lines 62 with the bit linecontact holes 58.

Next, the thickness of the contact conducting films 44 and the width ofthe sidewall oxide films 56 are optimized to satisfy the above-describedparameters. For example, when a thickness of the contact conductingfilms 44 is 0.05 μm, a width of the sidewall oxide films 56 is 0.12 μm,an interval of the capacitor opposed electrodes 54 in the direction ofthe word lines is 0.4 μm, and a width of the bit line contact holes 58is 0.16 μm.

The bit line contact holes 58 described here function to block etchingthe contact conducting films 44, etc. in the etching for the formationof the bit lines 62. Needless to say, if control of the etching isprecise, a width of the bit line contact holes 58 may be wider than thatof the bit lines 62.

By forming the bit line contact holes 58 of rectangular section which islengthy in the direction of the bit lines 62 as shown in FIGS. 48B andC, a minimum cell area can be realized. This cell area is 0.72 μm².

Then, a structure example of the peripheral circuit will be explained.

As shown in FIG. 49, decoders 94 and sense amplifiers 96 are formedrespectively on the opposed sides of a memory cell region. Thisarrangement of the decoders 94 and the sense amplifiers 96 enables aperipheral circuit to be arranged without any trouble even in a casethat no alignment allowance is taken to decrease a memory cell area.

In the present embodiment, the word lines and the bit lines are arrangedby a L/S of minimum processing dimensions, and it is impossible to bendthe bit lines 62 on the way. Accordingly, the twist bit line structurein which a pair of bit lines are twisted on each other on the way tosuppress interference therebetween. The use of the shield bit linestructure in which shield plates are provided on bit lines to suppressinterference therebetween unavoidably adds to a number of fabricationsteps.

By making a film thickness of bit lines 62 sufficiently smaller than agap between the bit lines 62, capacity coupling between the bit lines 62can be reduced, and interference between the bit lines 62 can bereduced. For example, bit lines 62 have a structure of W film (50nm)/TiN film (50 nm)/Ti film (30 nm) and a total film thickness of 0.13μm, whereby a film thickness of the bit lines 62 can be smaller than ahalf of a 0.3 μm gap between the bit lines 62. This works on theinterference between the bit lines 62.

Thus, according to the present embodiment, by optimizing the structureof the bit line contact holes, even in a case that the bit lines arearranged in minimum processing dimensions, an overlap allowance betweenthe bit line contact holes and the bit lines can be secured. Thesemiconductor storage device can have a much diminished memory cellarea.

The decoders and the sense amplifiers are arranged respectively on theopposed sides of the memory cell area, whereby even in a case that thememory cell area is diminished without any alignment allowance, aperipheral circuit can be arranged without any trouble.

Thirteenth Embodiment

The semiconductor storage device according to a thirteenth embodimentand the method for fabricating the same will be explained with referenceto FIGS. 50 to 55.

FIG. 50 is a plan view of the semiconductor storage device according tothe present embodiment which explain the structurethereof. FIG. 51 is adiagrammatic sectional view of the semiconductor storage device of FIG.50 along the line 51—51 in FIG. 50. FIGS. 52A-52D, 53A-53B, and 54A-54Bare sectional views of the semiconductor storage device in the steps ofthe method for fabricating the semiconductor storage device according tothe present embodiment, which explain the method. FIG. 55 is adiagrammatic sectional view of a variation of the semiconductor storagedevice according to the present embodiment, which explains the structurethereof.

In the semiconductor storage device according to the present embodimentand the method for fabricating the same, different methods for formingthe bit lines and the capacitors are applied to the semiconductorstorage device according to the eighth embodiment and the method forfabricating the same.

First, the structure of the semiconductor storage device according tothe present embodiment will be explained with reference to the plan viewof FIG. 50 and the sectional view of FIG. 51. FIG. 51 basically showsthe section along the line A-A′ in FIG. 50, but parts of bit lines 62and through-holes 38 are temporarily moved out. That is, FIG. 51 showsthe section along the line B-B′ in FIG. 50 and the section along theline A-A′ in FIG. 50 together.

A device region 14 is defined on a semiconductor substrate 10 by adevice isolation film 12. Source diffused layers 24 and drain diffusedlayers 26 are formed separately from each other in the device region 14.Gate electrodes 20 are formed through gate oxide films 16 onsemiconductor substrate 10 between the source diffused layers 24 and thedrain diffused layers 26. Thus, memory cell transistors are constitutedby the gate electrodes 20, the source diffused layers 24 and the draindiffused layers 26.

The bit lines 62 are arranged in the direction intersecting the gateelectrodes 20 and connected to the drain diffused layers 26 through thethrough-holes 38. Capacitor storage electrodes 46 are connected to thetop of the source diffused layers 24 through through-holes 40, andcapacitors are constituted by capacitor dielectric films 48 andcapacitor opposed electrodes 54 formed on the capacitor storageelectrodes 46. Wiring layers 70 are formed above the capacitors throughan inter-layer insulation film 64. A DRAM comprising 1-transistor and1-capacitor memory cells is constituted.

The gate electrodes 20, i.e., word lines, have a width of 0.2 μm andarranged at an interval of 0.3 μm. The through-holes 38, 40 have anopening diameter of 0.1 μm and spaced from the gate electrodes 20 by 0.1μm. The bit lines have a width of 0.2 μm and are arranged at an intervalof 0.3 μm. An overlap of the bit lines on the through-holes 38 is about0.05 μm, and a distance of the bit lines from the through-holes 40 isabout 0.1 μm. Thus, memory cells having a 0.5 μm² cell area areconstituted.

Then, the method for fabricating the semiconductor storage deviceaccording to the present embodiment will be explained.

A device isolation film of an about 300 nm-thickness is formed on themajor surface of the silicon substrate 10 by, e.g., the usual LOCOS todefine the device region 14. Then, an about 10 nm-thick gate oxide film16 is formed in the device region 14.

Subsequently, an about 150 nm-thick polycrystalline silicon filmcontaining a high concentration of P is grown by CVD, and thepolycrystalline silicon film is patterned by the usual lithography andetching to form the gate electrodes 20.

Then, with the device isolation film 12 and the gate electrodes 20 as amask, the source diffused layers 24 and the drain diffused layers 26 ofthe memory transistors are formed by implanting, for example, P ionsunder the conditions of a 20 keV acceleration energy and a 2×10¹³ ionscm⁻² dose (FIG. 52A).

Next, an about 50 nm-thick silicon oxide film and an about 200 nm-thickBPSG film are successively grown by CVD and then are reflowed toplanarize the surface to form an inter-layer insulation film 150.

Subsequently, an about 50 nm-thick polycrystalline silicon film 158 isdeposited by CVD and is patterned into an about 0.3 μm width by theusual lithography and etching (FIG. 52B).

Then, an about 100 nm-thick polycrystalline silicon film is deposited byCVD and etched vertically by RIE to form polycrystalline siliconsidewalls 160 on the sidewalls of the patterned polycrystalline siliconfilm 158. The polycrystalline silicon sidewalls 160 formed at a 0.3μm-width interval expose the inter-layer insulation film 150 by an about0.1 μm-width (FIG. 52C).

Next, with the polycrystalline silicon films 158 and the polycrystallinesilicon sidewalls 160 as a mask, the inter-layer insulation film 150 isetched to form the through-holes opened on the drain diffused layers 26and the through-holes 40 opened on the source diffused layers 24 (FIG.52D).

The thus-formed through-holes 38, 40 have an opening diameter which issubstantially equal to the interval of the polycrystalline siliconsidewalls 160, about 0.1 μm as described above.

In the present embodiment, the through-holes 38, 40 are opened with thepolycrystalline silicon films 158 and the polycrystalline siliconsidewalls 160 as a mask, whereby the processing is enabled at below aresolution limit of an exposure device. As in the method for fabricatingthe semiconductor storage device according to the eighth embodiment, thethrough-holes 38, 40 may be opened by electron-beam lithography. Byusing either method, the through-holes can have dimensions which cannotbe formed by the usual lithography.

Subsequently, an about 60 nm-thick polycrystalline silicon film, anabout 100 nm-thick tungsten silicide film and a silicon nitride film aredeposited by CVD and patterned by the usual lithography and etching, andthe bit lines 62 of a tungsten polycide structure whose top is coveredwith the silicon nitride films 156.

To pattern the bit lines 62, the polycrystalline silicon film 158 andthe polycrystalline silicon sidewalls 160 are patterned together, andburied conductors 162 of the polycrystalline silicon film are left inthe through-holes 40 (FIG. 53A).

The through-holes 40 are not essentially filled with the polycrystallinesilicon alone. For example, the polycrystalline silicon film and thetungsten silicide may be filled in the through-holes 40. As shown inFIG. 55, the polycrystalline silicon film, the tungsten silicide filmand the silicon nitride film may be filled in the through-holes 40.Either structure can be used without trouble because contact is made atthe entire bottoms of the through-holes 40.

It is preferable that an insulation film formed on the bit lines 62 areformed of silicon oxide film, whose dielectric constant is low, for thepurpose of decreasing parasitic capacitances. In a case, however, thatthe insulation film on the bit lines 62 is used as an etching stopper,it is difficult to use silicon oxide film. In a case that the insulationfilm is used as an etching stopper, it is most effective that alaminated film of silicon oxide film and a silicon nitride film isformed on the bit lines 62.

Then, an about 80 nm-thick silicon nitride film is deposited by CVD andetched vertically by RIE. Thus, sidewalls 164 are formed on thesidewalls of the bit lines 62, and the bit lines 62 are completelycovered with the silicon nitride films 156 and the sidewalls 164 (FIG.53B).

Next, an about 500 nm-thick polycrystalline silicon film is deposited byCVD and patterned by the usual lithography and etching to form thecapacitor storage electrodes 46 (FIG. 54A). By thus forming thecapacitor storage electrodes 46, the capacitor storage electrodes 46 canbe connected to the source diffused layers 24 without a masking step.One masking step can be omitted in comparison with the conventionalmethod.

Subsequently, an about 5 nm-thick silicon nitride film is deposited byCVD, and the surface of the silicon nitride film is oxidized to form thecapacitor dielectric films 48.

Then, an about 100 nm-thick polycrystalline silicon film is deposited byCVD and patterned by the usual lithography and etching to form thecapacitor opposed electrodes 54 (FIG. 54B).

Next, an about 300 nm-thick BPSG film is deposited by CVD and then isreflowed to form the inter-layer insulation film 154.

Subsequently, through-holes are formed in a peripheral circuit region(not shown), and then a metal material, such as tungsten or others isdeposited and patterned to form the wiring layers 70 (FIG. 55).

Thus, a DRAM comprising 1-transistor and 1-capacitor memory cells isconstituted.

In the present embodiment, the memory capacitor cells are high, and alarge height difference is present between the peripheral circuit regionand the memory cell region, whereby the wiring layers 70 on the memorycells have a relaxed line width and interval.

In the present embodiment, the capacitor storage electrodes 46 areconnected to the source diffused layers 24 through the buried conductors162 buried in the through-holes 40 formed simultaneously with theformation of the through-holes 38, which (the buried conductors 162) areformed simultaneously with the formation of the bit lines 62. As aresult, without adding a new step to the formation of the through-holes40, advantageously the silicon nitride films 156 on the bit lines 62 areexposed to an etching atmosphere for a reduced period of time.

In covering the tops and the sidewalls of the bit line 62 with theinsulation film, the buried conductors 164 are exposed, whereby, as inthe conventional method, it is not necessary to form the contactthrough-holes, using a masking step. One masking step can be omitted.

Fourteenth Embodiment

The semiconductor storage device according to a fourteenth embodimentand the method for fabricating the same will be explained with referenceto FIGS. 56 to 58B.

FIG. 56 is a diagrammatic sectional view of the semiconductor storagedevice according to the present embodiment, which explains the structurethereof. FIGS. 57A-57B and 58A-58B are sectional views of thesemiconductor storage device in the steps of the method for fabricatingthe same, which explain the method.

In the semiconductor storage device according to the thirteenthembodiment, the memory cell capacitors are so high that a large heightdifference between the peripheral circuit region and the memory cellregion is present. The wiring layers 70 on the memory cells must bedesigned on a relaxed wiring rule. The semiconductor storage deviceaccording to the present embodiment and the method for fabricating thesame can solve this problem.

The semiconductor storage device according to the present embodiment ischaracterized in that an inter-layer insulation film 152 is formed on aperipheral circuit region, and a height difference between a memory cellregion and the peripheral circuit region is small.

That is, in the peripheral circuit region the inter-layer insulationfilm has the three-layer structure of an inter-layer insulation films150, 152, 154, and the inter-layer insulation films 150, 154 constitutethe inter-layer insulation film in the memory cell region. Accordingly,the inter-layer insulation film of the peripheral circuit region isthicker by a thickness of the inter-layer insulation film 152, and aheight difference between the memory cell region and the peripheralcircuit region is small.

Then, the method for fabricating the semiconductor storage deviceaccording to the present embodiment will be explained.

The semiconductor storage device is fabricated up to bit lines 62 andburied conductors 162 by following the same steps as the method forfabricating the semiconductor storage device according to the thirteenthembodiment shown in FIGS. 52A to 53B (FIG. 57A).

Next, an about 300 nm-thick BPSG film is deposited by CVD and then isreflowed or polished to form an inter-layer insulation film 152 havingthe surface planarized.

Subsequently, by using the usual lithography, and etching which isstopped at a silicon nitride film, through-holes 166 are formed in theinter-layer insulation film 152, and the buried conductors 162 areexposed with the bit lines 62 covered with the silicon nitride film 156and sidewalls 164 (FIG. 57B).

Then, an about 20 nm-thick polycrystalline silicon film is grown by CVD,and the surface is polished to form capacitor storage electrodes 46 inthe openings 166. The capacitor storage electrodes 46 are connected tothe buried conductors 162 at an upper part in the through-holes 40 (FIG.58A).

In the polishing the method for fabricating the semiconductor storagedevice according to the ninth embodiment to the eleventh embodiment maybe used so that pulverized objects and a polishing agent do not intrudeinto the openings 166.

Then, the inter-layer insulation film 152 is etched by 50 nm by wetetching using, e.g., a hydrofluoric acid-based aqueous solution. Thethus etching of the top of the inter-layer insulation film 152 exposes alarger area of the capacitor storage electrodes 40, which increases acapacitance but increases a height difference between the memory celland the peripheral circuit region. It is preferable that the etching isnot conducted in a case that the height difference is significant.

Subsequently, the capacitor dielectric films 48, the capacitor-opposedelectrodes 54, the inter-layer insulation film 154 and the wiring layers70 are formed, and a DRAM comprising 1-transistor and 1-capacitor memorycells is constituted.

According to the method for fabricating the semiconductor storage deviceaccording to the present embodiment, a height difference in theinter-layer insulation film 154 between the memory cell region and theperipheral circuit region can be made small, which permits the wiringlayers 70 to be arranged on a more precise design rule than in thesemiconductor storage device according to the thirteenth embodiment.

As described above, according to the present embodiment, a heightdifference between the peripheral circuit region and the memory cellregion can be made small, which allows the design rule of the wiringlayers 70 to be micronized without adding to the number of thefabrication steps.

What is claimed is:
 1. A semiconductor device comprising: a firstconductor pattern formed over a semiconductor substrate; a firstinsulation film formed over the first conductor pattern; a secondinsulation film, formed of non-doped silicon oxide, formed over thefirst insulation film, having a substantially flat surface, and havingetching characteristics different from those of the first insulationfilm; a third insulation film formed over the second insulation film,and having etching characteristics different from those of the secondinsulation film; a fourth insulation film, formed of non-doped siliconoxide, formed over the third insulation film, and having etchingcharacteristics different from those of the third insulation film; anopening formed in the fourth insulation film, the third insulation film,the second insulation film, and the first insulation film, the openingbeing self-aligned with the first conductor pattern; and a secondconductor pattern formed in the opening.
 2. A semiconductor deviceaccording to claim 1, wherein each of the first insulation film and thethird insulation film is formed of silicon nitride.
 3. A semiconductordevice according to claim 1, wherein the first conductor pattern and thesecond conductor pattern are insulated from each other by the firstinsulation film.
 4. A semiconductor device according to claim 1, whereinthe second conductor pattern is electrically connected to thesemiconductor substrate.
 5. A semiconductor device according to claim 1,wherein the opening is formed down to the first conductor pattern, thesecond conductor pattern is electrically connected to the firstconductor pattern.
 6. A semiconductor device according to claim 1,wherein the first insulation film includes a film covering an uppersurface of the first conductor pattern and a side wall film covering aside wall of the first conductor pattern.
 7. A semiconductor deviceaccording to claim 1, further comprising: a third conductor patternformed over the fourth insulation film and electrically connected to thesecond conductor pattern.
 8. A semiconductor device according to claim1, wherein the fourth insulation film has a substantially flat surface.9. A semiconductor device comprising: a semiconductor substrate; a firstconductor formed over the semiconductor substrate; a first insulatorcovering the first conductor; a second insulator, formed of non-dopedsilicon oxide, formed over the first insulator, having different etchingcharacteristics from that of the first insulator, and having aplanarized surface; a third insulator formed over the second insulator;a fourth insulator, formed of non-doped silicon oxide, and formed overthe third insulator; a contact hole exposing a second conductor throughthe second, third and fourth insulators, the contact hole beingself-aligned with the first conductor; and a third conductor filled inthe contact hole, wherein the third conductor is electrically connectedto the second conductor.
 10. A semiconductor device according to claim9, wherein each of the first insulator and the third insulator is formedof silicon nitride.
 11. A semiconductor device according to claim 9,wherein the first conductor and the second conductor are insulated fromeach other by the first insulator.
 12. A semiconductor device accordingto claim 9, wherein the first insulator includes a film covering anupper surface of the first conductor and a side wall film covering aside wall of the first conductor pattern.
 13. A semiconductor devicecomprising: a semiconductor substrate; an impurity doped region formedin the semiconductor substrate; a first conductor formed over thesemiconductor substrate; a first insulator covering the first conductor;a second insulator, formed of non-doped silicon oxide, formed over thefirst insulator, having different etching characteristics from that ofthe first insulator and having a planarized surface; a third insulatorformed over the second insulator; a fourth insulator, formed ofnon-doped silicon oxide, formed over the third insulator, having aplanarized surface; a self-aligned contact hole exposing the impuritydoped region through the second, third and fourth insulators; and asecond conductor filled in the self-aligned contact hole, wherein thesecond conductor is electrically connected to the impurity doped region.14. A semiconductor device according to claim 13, wherein each of thefirst insulator and the third insulator is formed of silicon nitride.15. A semiconductor device according to claim 13, wherein the firstconductor and the second conductor are insulated from each other by thefirst insulator.
 16. A semiconductor device according to claim 13,wherein the first insulator includes a film covering an upper surface ofthe first conductor and a side wall film covering a side wall of thefirst conductor.